Depends on the situation, last year on my first bird I was set up a ways from most roost sites and was staying right on the farm not 200 yards from my set up, got out right at sunrise, birds were hammering all over, shot my bird at like 9am!
Second bird I had to set my blind up in a wide open field where birds could see, got in an hour before shooting time, set the blind and dekes in the pitch black and killed my bird a couple hours later!
If I am going in cold I want to be there half hour before shooting time!