What is the time period that the most American surfers are online?

Most "surfers" are online when they are at work/school.
8:00AM - 4:00PM would be my guess. (Any location)

about 4-5 in the afternoon this is peak load for America as people are at home as well as business are running and everyone is trying to use appliances at the same time...
You will also find blackouts are most common to occur during this time period as well.