2 yrs back I was in my stand in the pitch black of the morning and listened for over 10 minutes as a deer came up the hill and walked right in front of me, maybe 20yrds out. I couldn't see a thing, but it knew something was wrong. I could tell it was doing the head bob snort and pawing the ground, but eventually it just walked off... or at least that's what it all sounded like.

Therefore I try to be in the stand for a minimum of 1/2hr before legal shooting hours... 45-60 min is better.