Welcome to the addiction!
A couple of questions for you and a few answers, one to a question you didn't ask.
First, what part of OK? The Arbuckle Mountains, the Panhandle, or somewhere in between? All will require slightly different techniques.
It sounds as if you're hunting in thick brush/cover if they're within 30 yards and you can't see them. That's shotgun territory and plan on fast shooting.
If the brush is thick, you may be tempted to turn your head, trying to locate them. You still have to move really slowly if you do that because you may not be able to make them out through the brush, but they don't need a full picture of you to hang up, all they need is movement that isn't consistent with a small prey creature being killed.
As Dave (DSheetz) mentioned, the amount of time spent on the stand has too many variables to give a set answer.
Typically, I am on the stand at least 20 minutes before I ever start calling, letting nature settle down. There are exceptions, but that is my standard.
I always park my vehicle in a hidden spot from my stand, and try to position it so any wind won't blow the odor of it into my calling pattern.
Learning the coyotes language is the best thing you can do.
Holwlers are great for more than just locating coyotes, a good one, such as Crit'r Calls "Song Dog" will give you the options for most vocalizations.
Simple mouse squeaks will gather more attention than you would expect.
Dying rabbit calls are used more often than any other and have educated more coyotes than any other sounds.
Like Dave, I didn't learn this overnight, but through many days, weeks, and years of trial and error.
A ton of bad judgment calls have given rise to much better judgment when it comes to calling coyotes.
I hope some of this is of use to you and any others lurking.
Best wishes for your success!
Ed