It is the time between trades. I believe it is explained in the
forex autopilot manual, and somewhere else on this forum (but unfortunately I don't remember which thread so I suggest you use the "search" function at the top of the forum).
I would suggest you leave the stop time to the default setting until you fully understand what all the settings do.
Some forum members advocate setting a higher StopTime to prevent
FAP getting itself stuck in a bad trade, so look into that when you get the chance - once again you should find plenty of threads regarding custom FAP settings and such.