I noticed something similar during meditation: I had set up the stopwatch on my phone so that I did not have to wonder how many time had passed. It would just ring when 30 minutes had passed. However, when the phone was just lying next to me, I would compulsively check the time on the phone every few minutes. Only when I moved the phone to the other side of the room did I stop caring about the time passed (at least for the most part).