Evenings over here seem a bit slow sometimes, which is probably the small hours of the morning in the US where a large percentage of the users seem to be based.
Weekends are a bit slow sometimes, although I don't often get a chance to even look at GH on Saturdays, and sometimes not until late afternoon on Sundays (today, for example).
Looks like I do most of my posting between 8pm and 9pm, which would be about right - that's evening between dinner and bed.