Same here in Iowa. I'll be back out today at 3:30. Pretty dark at 6:30 here right now. I would say a good 3 hours will allow you to get in. Depends on what you are hunting in regards to feeding/bedding areas too.
Deer in my woods usually start lurking around a few hours before dark. I try to get out after having lunch by 3pm. This gives you a chance to get to the stand quietly and settle in before deer are moving. Earlier never hurts. I like afternoon hunts because you know you have a set cutoff time unlike morning hunts where boredom usually prevails.
Well I hunt all day now.. I hunted yesterday all day and saw 3 doe.. They all came out between 2:45-3:05 pm.. Weird right? This year I have seen soo many deer eating on the side of the road in the heat of the day... Its been an interesting year for me...
I pay close attention to my trailcam pics & like to be in my stand ready to hunt at least half an hour before I have seen pics on my trailcams. Basically it comes down to roughly 3 hours before sunset. During rut all bets are off though.