I've only had 1 shot not drop the deer instantly.
last year in the pea soup fog with him quartering away at 25-30 yards I had the scope on 9x by accident and hit forward on the shoulder, he thrashed for a few minutes till I put a round through his neck.

Regardless, even if the deer is down where I can see it, I give 30 min. minimum. If it ran off with a good hit: 30-45 min. With an 'iffy' I'd say 2-3 hours. Because I was with my buddy in Ozona when he gut shot a nice buck, and we only waited about 1-1.5 hours, and spooked him about 50 yards from where he was hit. Given a little more time he woulda expired right there. As it was we never saw him again.