As to when to come back to an area after you called in, I agree with Roy. Coyotes can have a pretty decent size home area, around 6 sq. miles in some areas. Obviously, if they aren't in hearing range the first time you call you aren't going to spook them. If you do spook them while calling, wait a week or so and go back in with a different call and set-up. A different stand location is a good idea, too.
As for the second, depends on your location and if you want to keep the pelts or not. I have seen Montana dogs starting to look good the first of Oct. If you don't care about the pelts, get going before the regular hunting season gets underway. The pups are about full grown and are still stupid. Hunting season wises them up, the ones still left. Otherwise, do like Roy does and wait till after Halloween.