Depends on the body of water. Overall bigger mid to large lakes are best mid morning through early afternoon. The missouri river for me typically is best early morning and late evening year around. On pretty much any lake or river there is always a flurry of activity right before sundown. Walleye bite better in the early morning and late evening during the winter but that is not the case in spring, summer and fall. This is just a generalization however and not a stead fast rule. There has been times fish were practically jumping in the boat right away at 7am and completely shut down by 10am during the open water season. I try to get on the water by 7am everytime I go in the boat not only to not miss out on an early bite but I figure if I am spending the gas money to go to the lake I want to get a full day in. Also the wind usually picks up as the day goes on so it is nice to get some fishing in relatively calm conditions.