For me, this all depends on my cover set up and what the wind is doing in relation from my stand to the animal. If I'm in a stand and the concealment is good, the wind is in my face and the animal is coming 'towards' me--then I wait for the best shot opportunity, before even drawing my bow.
On the other hand, in areas where that cover is not as good, my game plan changes. 'Movement' becomes a serious factor, standing still--you'll either get the chance, sometimes you will not. I choose to execute shot when I am most confident & comfortable--otherwise I'll pass.
Holding a bow at full draw (for myself) in excess of 20 seconds isn't something I like doing. It becomes uncomfortable, my chemical transmitters starts second guessing myself, holding the bow at full draw, waiting, moving the pin searching for the kills zone--I've got a shot, I don't have a shot, too many factors to think about, then the hand starts to wobble, you're running short of air--a perfect scenario for what could be a terrible 'punch' shot!!