Strangely, I have noticed the best time to play (at least for me) is between 4pm-7pm US Central Time. Three things could be the reason for this...
A) People getting off work, and want to donk off some money before dinner.
or
B) It is past midnight across the pond and some of our Euro friends had one to many at the pub and can't see straight.
or
C) Both A&B
I am leaning towards C.
I think it is a bad idea to play in the "wee hours" because everyone thinks this is the weakest time. When you think you are playing against fish, you end up playing against other sharks. This is all theory, of course. I could be wrong. I am often.