Due to time zones, I doubt there's really a clear time that would fit well. Besides, people are going to procrastinate one way or another. More importantly, if

Due to time zones, I doubt there's really a clear time that would fit well. Besides, people are going to procrastinate one way or another. More importantly, if you are spending too much time on the site, then just stop loading it. Nobody else is making you reload the page X times a day.