There is no finite line or amount that defines "too-much". You have to let the bird tell you.

A lot of folks call every single time a bird gobbles, and then they call again.

I have a general rule of thumb.... if I KNOW that a bird has responded directly to my call.... I will usually wait about 3-4 minutes and see if he gobbles again... if he gobbles on his own... I'll usually respond with a more excited yelp, maybe even a cutt..... if he responds to that... then I shut up until further notice... no matter how much he gobbles. Usually in that instance, he's dead in less than 20 minutes. You have to know your hunting ground and try and pin point exactly where he is, and figure what is between the two of you. If there is a fence or a creek... then the odds are againest you. Listen to where he is moving when he gobbles.... getting closer... getting further away.... no moving at all?

Usually the result of over-calling is a bird hanging up... or stopping short... usually at least 80 yards out from you... often more. When you over call... the gobbler thinks the hen is hot and is going to come to him... since thats what happens naturally 90% of the time. What you have to do is keep him curious and keep him searching. Often when a bird hangs up... he will stand in one spot and gobble his damn head off... if he is gobbling every 30 seconds-1 minute and not moving.... odds are he is hung up... doesn't always mean you over did it... but it means you have to make a move.