For me it depends on what I was doing the day before and how much time I have to hunt that day. I've gone 30 min before sunrise and gone 30 min after sunrise and taken deer both ways.

anything over 30 mins before daylight is overkill IMHO, but 20 - 30 mins before light what i shoot for, hell if i get out there too early im freezing by the time daylight hits, which just makes me want to get out of the stand that much sooner

I usually get to my ground blind 2 hourrs before light. On warm nights I will even sleep overnight in the blind. I have nothing better to do

Before light at least 30 minutes. If you spoke a deer you have a beter chance of them not knowing what it was if they didnt smell you.