diff --git a/Project.toml b/Project.toml
index ec4986f..6a322c7 100644
--- a/Project.toml
+++ b/Project.toml
@@ -1,7 +1,7 @@
 name = "ACTRModels"
 uuid = "c095b0ea-a6ca-5cbd-afed-dbab2e976880"
 authors = ["itsdfish"]
-version = "0.8.1"
+version = "0.8.2"
 
 [deps]
 ConcreteStructs = "2569d6c7-a4a2-43d3-a901-331e8e4be471"
diff --git a/src/ACTRModels.jl b/src/ACTRModels.jl
index ff5dfe4..bbe364e 100644
--- a/src/ACTRModels.jl
+++ b/src/ACTRModels.jl
@@ -67,10 +67,10 @@ module ACTRModels
     export spreading_activation!, match, compute_RT, retrieval_request, get_subset
     export first_chunk, posterior_predictive, find_index, find_indices, get_mean_activations
     export get_visicon, get_iconic_memory
-    export get_time, add_time, reset_time!, rnd_time
+    export get_time, set_time!, add_time!, reset_time!, rnd_time
     export blend_chunks, blended_activation
 
     include("Structs.jl")
-    include("MemoryFunctions.jl")
     include("Utilities/Utilities.jl")
+    include("MemoryFunctions.jl")
 end
diff --git a/src/MemoryFunctions.jl b/src/MemoryFunctions.jl
index 2f821a0..bcb6fe1 100644
--- a/src/MemoryFunctions.jl
+++ b/src/MemoryFunctions.jl
@@ -52,6 +52,24 @@ Computes baselevel activation for all chunks according exact equation.
 """
 baselevel!(actr) = activation!.(actr, memory.memory)
 
+"""
+    compute_activation!(actr::AbstractACTR, chunks::Vector{<:Chunk}; request...) 
+
+Computes the activation of a vector of chunks. By default, current time is computed with `get_time`.
+
+# Arguments
+
+- `actr::AbstractACTR`: an `ACTR` object
+- `chunks::Vector{<:Chunk}`: a vector of chunks.
+
+# Keywords
+
+- `request...`: optional keywords for the retrieval request
+"""
+function compute_activation!(actr::AbstractACTR, chunks::Vector{<:Chunk}; request...)
+    return compute_activation!(actr, chunks, get_time(actr); request...)
+end
+
 """
     compute_activation!(actr::AbstractACTR, chunks::Vector{<:Chunk}, cur_time::Float64=0.0; request...) 
 
@@ -61,13 +79,13 @@ Computes the activation of a vector of chunks
 
 - `actr::AbstractACTR`: an `ACTR` object
 - `chunks::Vector{<:Chunk}`: a vector of chunks.
-- `cur_time::Float64=0.0`: current simulated time in seconds
+- `cur_time::Float64`: current simulated time in seconds
 
 # Keywords
 
 - `request...`: optional keywords for the retrieval request
 """
-function compute_activation!(actr::AbstractACTR, chunks::Vector{<:Chunk}, cur_time::Float64=0.0; request...)
+function compute_activation!(actr::AbstractACTR, chunks::Vector{<:Chunk}, cur_time::Float64; request...)
     @unpack sa = actr.parms
     sa ? cache_denomitors(actr) : nothing
     # compute activation for each chunk
@@ -78,7 +96,26 @@ function compute_activation!(actr::AbstractACTR, chunks::Vector{<:Chunk}, cur_ti
 end
 
 """
-    compute_activation!(actr, chunk::Chunk, cur_time=0.0; request...) 
+    compute_activation!(actr, chunk::Chunk; request...) 
+
+Computes the activation of a chunk. By default, current time is computed 
+with `get_time`.
+
+# Arguments
+
+- `actr`: actr object
+- `chunk::Chunk`: a chunk.
+
+# Keywords
+
+- `request...`: optional keywords for the retrieval request
+"""
+function compute_activation!(actr, chunk::Chunk; request...)
+    return compute_activation!(actr, chunk, get_time(actr); request...)
+end
+
+"""
+    compute_activation!(actr, chunk::Chunk, cur_time; request...) 
 
 Computes the activation of a chunk
 
@@ -86,32 +123,48 @@ Computes the activation of a chunk
 
 - `actr`: actr object
 - `chunk::Chunk`: a chunk.
-- `cur_time=0`: current simulated time in seconds
+- `cur_time`: current simulated time in seconds
+
+# Keywords
+
+- `request...`: optional keywords for the retrieval request
+"""
+compute_activation!(actr, chunk::Chunk, cur_time; request...) = compute_activation!(actr, [chunk], cur_time; request...)
+
+"""
+    compute_activation!(actr::AbstractACTR; request...)
+
+Computes the activation of all chunks in declarative memory. By default, current time is computed
+with `get_time`.
+
+# Arguments
+
+- `actr::AbstractACTR`: an `ACTR` object
 
 # Keywords
 
 - `request...`: optional keywords for the retrieval request
 """
-compute_activation!(actr, chunk::Chunk, cur_time=0.0; request...) = compute_activation!(actr, [chunk], cur_time; request...)
+compute_activation!(actr::AbstractACTR; request...) = compute_activation!(actr, actr.declarative.memory, get_time(actr); request...)
 
 """
-    compute_activation!(actr::AbstractACTR, cur_time::Float64=0.0; request...)
+    compute_activation!(actr::AbstractACTR, cur_time::Float64; request...)
 
 Computes the activation of all chunks in declarative memory
 
 # Arguments
 
 - `actr::AbstractACTR`: an `ACTR` object
-- `cur_time::Float64=0.0`: current simulated time in seconds
+- `cur_time`: current simulated time in seconds
 
 # Keywords
 
 - `request...`: optional keywords for the retrieval request
 """
-compute_activation!(actr::AbstractACTR, cur_time::Float64=0.0; request...) = compute_activation!(actr, actr.declarative.memory, cur_time; request...)
+compute_activation!(actr::AbstractACTR, cur_time::Float64; request...) = compute_activation!(actr, actr.declarative.memory, cur_time; request...)
 
 """
-    activation!(actr, chunk::Chunk, cur_time=0.0; request...) 
+    activation!(actr, chunk::Chunk, cur_time; request...) 
 
 Computes the activation of a chunk
 
@@ -119,7 +172,7 @@ Computes the activation of a chunk
 
 - `actr`: an `ACTR` object
 - `chunk::Chunk`: a chunk.
-- `cur_time=0`: current simulated time in seconds
+- `cur_time`: current simulated time in seconds
 
 # Keywords
 
@@ -286,6 +339,21 @@ function count_values(chunk, value)
     return count(x -> x == value, values(chunk.slots))
 end
 
+
+"""
+    update_recent!(actr, chunk)
+
+Adds a new timestamp to chunk and removes oldest timestamp if
+length equals k. By default, current time is computed with `get_time`.
+
+# Arguments
+- `actr`: an ACT-R model object 
+- `chunk`: memory chunk object
+"""
+function update_recent!(actr::AbstractACTR, chunk)
+    return update_recent!(chunk, get_time(actr))
+end
+
 """
     update_recent!(chunk, cur_time)
 
@@ -307,22 +375,41 @@ function update_recent!(chunk, cur_time)
 end
 
 """
-    retrieval_prob(actr::AbstractACTR, target::Array{<:Chunk,1}, cur_time=0.0; request...)
+    retrieval_prob(actr::AbstractACTR, target::Array{<:Chunk,1}; request...)    
+
+Uses the softmax approximation to compute the retrieval probability of retrieving a chunk.
+By default, current time is computed from `get_time`.
+
+# Arguments
+
+- `actr::AbstractACTR`: an ACT-R object
+- `target::Array{<:Chunk,1}`: a vector chunks in the numerator of the softmax function
+
+# Keywords
+
+- `request...`: optional keyword pairs representing a retrieval request
+"""
+function retrieval_prob(actr::AbstractACTR, target::Array{<:Chunk,1}; request...)
+    return retrieval_prob(actr, target, get_time(actr); request...)
+end
+
+"""
+    retrieval_prob(actr::AbstractACTR, target::Array{<:Chunk,1}, cur_time; request...)
 
 Computes the retrieval probability of one chunk from a set of chunks defined in `target`.
 Retrieval probability is computed with the softmax approximation.
 
 # Arguments
 
-* `actr::AbstractACTR`: an actr object
-* `target::Array{<:Chunk,1}`: a vector chunks in the numerator of the softmax function
-* `cur_time=0.0`: current time in seconds
+- `actr::AbstractACTR`: an actr object
+- `target::Array{<:Chunk,1}`: a vector chunks in the numerator of the softmax function
+- `cur_time`: current time in seconds
 
 # Keywords
 
-* `request...`: optional keywords for the retrieval request
+- `request...`: optional keywords for the retrieval request
 """
-function retrieval_prob(actr::AbstractACTR, target::Array{<:Chunk,1}, cur_time=0.0; request...)
+function retrieval_prob(actr::AbstractACTR, target::Array{<:Chunk,1}, cur_time; request...)
     @unpack τ,s,noise = actr.parms
     σ = s * sqrt(2)
     chunks = retrieval_request(actr; request...)
@@ -340,6 +427,25 @@ function retrieval_prob(actr::AbstractACTR, target::Array{<:Chunk,1}, cur_time=0
     return prob,fail
 end
 
+"""
+    retrieval_prob(actr::AbstractACTR, chunk::Chunk; request...)
+
+Uses the softmax approximation to compute the retrieval probability of retrieving a chunk.
+By default, current time is computed from `get_time`.
+
+# Arguments
+
+- `actr::AbstractACTR`: an ACT-R object
+- `chunk::Chunk`: a chunk
+
+# Keywords
+
+- `request...`: optional keyword pairs representing a retrieval request
+"""
+function retrieval_prob(actr::AbstractACTR, chunk::Chunk; request...)
+    return retrieval_prob(actr, chunk, get_time(actr); request...)
+end
+
 """
     retrieval_prob(actr::AbstractACTR, chunk::Chunk, cur_time=0.0; request...)
 
@@ -349,13 +455,13 @@ Uses the softmax approximation to compute the retrieval probability of retrievin
 
 - `actr::AbstractACTR`: an ACT-R object
 - `chunk::Chunk`: a chunk
-- `cur_time=0.0`: current simulated time in seconds
+- `cur_time`: current simulated time in seconds
 
 # Keywords
 
 - `request...`: optional keyword pairs representing a retrieval request
 """
-function retrieval_prob(actr::AbstractACTR, chunk::Chunk, cur_time=0.0; request...)
+function retrieval_prob(actr::AbstractACTR, chunk::Chunk, cur_time; request...)
     @unpack τ,s,noise = actr.parms
     σ = s * sqrt(2)
     chunks = retrieval_request(actr; request...)
@@ -372,7 +478,26 @@ function retrieval_prob(actr::AbstractACTR, chunk::Chunk, cur_time=0.0; request.
 end
 
 """
-    retrieval_probs(actr::AbstractACTR, cur_time=0.0; request...)
+    retrieval_probs(actr::AbstractACTR; request...)
+
+Computes the retrieval probability for each chunk matching the retrieval request. By default,
+current time is computed from `get_time`. 
+
+# Arguments
+
+- `actr::AbstractACTR`: an actr object
+
+# Keywords
+
+- `request...`: optional keyword pairs representing a retrieval request
+"""
+
+function retrieval_probs(actr::AbstractACTR; request...)
+    return retrieval_probs(actr, get_time(actr); request...)
+end
+
+"""
+    retrieval_probs(actr::AbstractACTR, cur_time; request...)
 
 Computes the retrieval probability for each chunk matching the retrieval request.
 
@@ -385,7 +510,7 @@ Computes the retrieval probability for each chunk matching the retrieval request
 
 - `request...`: optional keyword pairs representing a retrieval request
 """
-function retrieval_probs(actr::AbstractACTR, cur_time=0.0; request...)
+function retrieval_probs(actr::AbstractACTR, cur_time; request...)
     @unpack τ,s,noise = actr.parms
     σ = s * sqrt(2)
     chunks = retrieval_request(actr; request...)
@@ -457,6 +582,22 @@ function update_chunk!(chunk, cur_time)
     return nothing
 end
 
+"""
+    add_chunk!(actr::AbstractACTR; slots...)
+
+Adds new chunk to declarative memory or updates existing chunk with new use. The default time is
+computed from `get_time`.
+
+# Arguments 
+
+- `actr::AbstractACTR`: an ACT-R model object
+
+# Keywords
+
+- `slots...`: optional keyword arguments corresponding to slot-value pairs, e.g. name=:Bob
+"""
+add_chunk!(actr::AbstractACTR; slots...) = add_chunk!(actr.declarative, get_time(actr); slots...)
+
 """
     add_chunk!(memory::Declarative, cur_time=0.0; act=0.0, slots...)
 
@@ -497,7 +638,7 @@ Adds new chunk to declarative memory or updates existing chunk with new use
 
 - `slots...`: optional keyword arguments corresponding to slot-value pairs, e.g. name=:Bob
 """
-add_chunk!(actr::AbstractACTR, cur_time=0.0; slots...) = add_chunk!(actr.declarative, cur_time; slots...)
+add_chunk!(actr::AbstractACTR, cur_time; slots...) = add_chunk!(actr.declarative, cur_time; slots...)
 
 """
     get_chunks(memory::Vector{<:Chunk}; criteria...)
@@ -811,20 +952,38 @@ function modify!(c::NamedTuple; args...)
 end
 
 """
-    retrieve(actr::AbstractACTR, cur_time=0.0; request...)
+    retrieve(actr::AbstractACTR; request...)
+
+Retrieves a chunk given a retrieval request. By default, current time is 
+computed with `get_time`.
+
+# Arguments 
+
+- `actr`: an ACT-R object
+
+# Keywords
+
+- `request...`: optional keyword arguments representing a retrieval request, e.g. person=:bob
+"""
+function retrieve(actr::AbstractACTR; request...) 
+    return retrieve(actr, get_time(actr); request...)
+end
+
+"""
+    retrieve(actr::AbstractACTR, cur_time; request...)
 
 Retrieves a chunk given a retrieval request
 
 # Arguments 
 
 - `actr`: an ACT-R object
-- `cur_time=0.0`: current simulated time in seconds
+- `cur_time`: current simulated time in seconds
 
 # Keywords
 
 - `request...`: optional keyword arguments representing a retrieval request, e.g. person=:bob
 """
-function retrieve(actr::AbstractACTR, cur_time=0.0; request...)
+function retrieve(actr::AbstractACTR, cur_time; request...)
     @unpack declarative,parms = actr
     arr = Array{eltype(declarative.memory),1}()
     chunks = retrieval_request(actr; request...)
@@ -931,8 +1090,7 @@ is only supported for numeric slot-values.
 - `request...`: optional keywords for the retrieval request
 """
 function blend_chunks(actr; request...) 
-    t = get_time(actr)
-    return blend_chunks(actr, t; request...) 
+    return blend_chunks(actr, get_time(actr); request...) 
 end
 
 """
diff --git a/src/Structs.jl b/src/Structs.jl
index d13f454..c4d78a5 100644
--- a/src/Structs.jl
+++ b/src/Structs.jl
@@ -264,6 +264,7 @@ function Base.show(io::IO, ::MIME"text/plain", chunks::Vector{<:Chunk})
     table = [chunk_values(chunk) for chunk in chunks]
     table = hcat(table...)
     table = permutedims(table)
+    table = isempty(chunks) ? fill(Missing, 1, length(chunk_fields)) : table 
     return pretty_table(
         table;
         title="Chunks",
diff --git a/src/Utilities/Utilities.jl b/src/Utilities/Utilities.jl
index 1cc9a8a..7146248 100644
--- a/src/Utilities/Utilities.jl
+++ b/src/Utilities/Utilities.jl
@@ -319,10 +319,13 @@ end
 get_time(actr::AbstractACTR) = get_time(actr.scheduler)
 get_time(scheduler) = scheduler.time 
 
-add_time(actr::AbstractACTR, t) = add_time(actr.scheduler, t)
-add_time(scheduler, t) = scheduler.time += t
+add_time!(actr::AbstractACTR, t) = add_time!(actr.scheduler, t)
+add_time!(scheduler, t) = scheduler.time += t
 
 reset_time!(actr::AbstractACTR) = reset_time!(actr.scheduler)
 reset_time!(scheduler) = scheduler.time = 0.0
 
+set_time!(actr::AbstractACTR, t) = set_time!(actr.scheduler, t)
+set_time!(scheduler, t) = scheduler.time = t
+
 rnd_time(μ) = rand(Uniform(μ * (2/3), μ * (4/3)))
\ No newline at end of file