With a stopwatch you are going to get only one start and stop time, if you need multiple timings you are going to have to use additional resources. Generally you can start and stop a stopwatch in your pocket because you don't have to LOOK at it. For additional timings you might also reference your watch or count off the seconds in your head. This is why it is infinitely easier to do this stuff with a DVR and giving yourself start and stop cues for the timings to be measured on playback. "Bump" when you come in the door (or the real time), "cough" when you join the line, the greeting by you or the employee to start an interaction timing, a "Thank you" from you when the receipt and or product is presented to mark an ending time, etc.
