The stopwatch is a feature in Show Pro that allows the user to time a segment, a presenter or anypart of the show flow the user needs timed. You can find this feature in both Rehearsal Mode and Show Mode
You can attach an automatic trigger for a stopwatch in the timer column for any cue. Simply press the + button and check attach stopwatch. You will see a symbol of a clock in the top corner of the cell after you attach the stopwatch.