Coding time durations

Hey guys -

trying to code for a duration of time - mm:ss:ms - finding it a little tricky as i haven't done it before. ANy help would be great. Thanks.

# time difference example showing results in seconds
# Sys.sleep(20) creates a pause of 20 seconds
my_time <- Sys.time()
Sys.sleep(20)
my_next_time <- Sys.time()
difftime(my_time, my_next_time, units = "secs")

If you search for date & time variables in R you will see there are several classes. You'll have to map the features vs complexity for each type compared to what you are trying to accomplish.