If an old hen begins calling, it almost pays to scare her away and then sit down again. The poults are deeply imprinted to her voice and your unknown voice will often be disregarded. 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.