The simple answer is from the time you can see to shoot until legal quitting time wherever you're hunting! Up here in MI we can hunt until it's darn near dark in May and I've killed good birds right up until almost quitting time. The older I get the more I hate the early morning wakeups so I do that a day or two and then sleep in a day or two and don't go out until I can't sleep any longer. If you don't get a Tom off the roost in the first hour, the longer you stay out the better chance you have after the hens start going to their nests the middle of the morning and the Toms have to start looking for new company.