There is some sort of internal clock, I guess. I just get a feeling when it's been too long with out a sell. Once he drops from all teeth one notch down to a grin, I give it one more tick or two before I back out of that one and go to another one. He goes from grin to pissed quickly so I nix it before that point. I think it is key to move from hard selling one to another but I still go back to the one I just hard sold and try it again even if it was successful the first time. If it's someone I really want, one hour is the minimum and I try to get more. Sometimes it is difficult though.