There is nothing consistence about when a flock will begin to assemble. Many start to reassemble in a matter of a few minutes. Other flocks may take a half-hour to several hours before they begin calling. Patience is a real virtue when calling turkeys. A yelp call is similar to an old hen is also effective.
Some birds call frequently with long uninterrupted yelps, while others only yelp a couple of times.
Often just a kee-kee will be heard. Once an approaching turkey is spotted, it's best not to call again unless the bird begins to move away from you. Wild turkeys have a tremendous ability to pinpoint sounds and if they do not see a turkey from the calling area they may leave. Do not raise your shotgun quickly. Very often, quick movements will alarm the bird and it will flush leaving you with a hurry-up shot.