There was a very good report about what times people were searching Google. If I remember correctly the slowest time is around 6am GMT. I would guess that it peaks at around 2-4pm GMT as this is my average peak for UK sites while the Americans are logging on when they reach their desks.
9:13 am on Apr 24, 2004 (gmt 0)
Given the rapidity with which the Chinese and Indians are getting on line I would say that whatever the time may be now ..within 2 years it will be friday evening around 15.00 gmt and closely followed by the same time on a Sunday ( when the kids have finished their homework and hit the chat boards! ).....