This is a subject I' ve always found interesting. Very few people I know get out in the woods before the eastern sky starts getting light. They go tromping into the woods when it is light enough for them to see and also for the birds on the roost to see them! Then they wonder why the birds fly down and go the other way. I like to be in the woods and set up well before the first hint of light in the sky, even on a scouting trip. Slipping in under the cover of darkness has worked wonders for me over the years. The earliest I have heard them gobbling here in N. Missouri this spring is around 5:30 but it is getting lighter earlier every morning so the gobbling will start earlier every day as the season progresses.