It all depends. I usually get to a listening spot and start with the owl call right away, early. Then try every 10 minutes or so. You are not gonna scare them or anything. Owls hoot at all hours of the night anyways. I've had times when the wont gobble till right before flydown, and also had times when I've gotten out of my car at like 4:10 and one was already going off. That was on a full moon night and doesn't happen alot but I say go ahead and give the owl call a try.