When I first started calling many years ago I was over educated LOL, I would sit for almost an hour if I did not see or hear anything but knew full well animals were in the area. Thru trial, error and a few success, my best time at a set in open country is about 20 minutes max.
Out here you can see for literally miles and waych dogs move in on you for hundreds of yards if your on top of the game.
I've had them come in less than minutes and just when I'm getting up to leave, but far and above if dogs are in the area they will respond is some attitude in less than 1o minutes here.
Heavy cover probably throws a wrench into this cause they can move in closer with out you knowing it so you really don't know how long they been there, in this instance I would choose a shooting lane over time of set for priority, then time it out for 20 minutes or so and move on.
I'd rather make 20 or so semi productive stands then only two or three long ones which may produce or not because of time.