I've done it both ways for a lot of years, well, not so much in the past 20, and haven't found it makes a difference, but I definitely spook fewer deer going in at first light. I hunt big woods and usually my stands are quite far in so I can start walking in the dark, but it's gray light by the time I'm a couple hundred yards from my stand.
Keep shooting hours in mind, too. For example, in my state, they're one-half hour before sunrise to one-half hour after sunset. If you're sitting in your stand with a strung bow before or after those times, you're hunting illegally.