I'd like to be about where I want to start hunting by around 5:30 in most cases (Western Middle TN), but it also depends on the terrain I'm hunting, and just how I'm hunting. If I'm hunting on the higher plateau-like areas or higher ridgelines, I start about 30 minutes sooner than when I'm hunting in some of the valleys that come off an eastern ridgeline.
Keep in mind the woods are really open right now, and a roosted turkey may be able to see you several hundred yards away if you're moving after it's already light. Situation can be much different once we get some foliage.