Anecdotally, the number of votes and comments correlates well with work hours around the world, at least on weekdays.
I did some ballpark estimations by charting timezones on a UTC timeline.
Times when multiple large, English-speaking timezones overlap are the ones with the most activity. This works out so that 7:00 -> 17:00 UTC are fairly busy as Europe and either of India or US Eastern are at work; the contribution of US Pacific continues a good amount of activity until 0:00 UTC.
Between the hours of 1:00 UTC and 2:30 UTC, India hasn't woken up yet, and it's lunch hour for eastern Australia.
One day I hope to obtain some actual numbers to check this hypothesis.