The advanced_delay plug-in delays the experiment for a pre-specified average duration plus a random margin.
Duration is the average duration of the delay in milliseconds.
Jitter is the size of the variation in the delay in milliseconds.
Jitter mode is the how the jitter is calculated:
Standard deviation will draw the variation from a Gaussian distribution with Jitter as the the standard deviation.
Uniform will draw the variation in duration from a uniform distribution.