This only applies if the test mix is based on user pace. Set to true if you want to apply a normal distribution to delays ...

This only applies if the test mix is based on user pace.  Set to true if you want to apply a normal distribution to delays in the user pacing mix.  For example, if you have a test which is set up to execute 2 times per hour and this property is set to false, then the second test will execute 30 minutes after the start of the first test.  If set to true, the delay between the first and second test will be determined by applying a normal distribution to 30 minutes.