I spend 10 - 30 minutes a day training my setter or until she gets it right. I often call her during playing times as sometimes she'll exploring out of sight. So, no I don't think that's a problem. Perhaps it's not breaking the time up into less time spent more sessions?

As to my method, here is what I do. I heel her for about 20-30 feet then woah her with the whistle. Then walk back, forwards, around her to make sure she stays put. Then I call her to me using the whistle. I heel her and repeat the process. We usually do this several times until we reach the car after play. Should I use the collar (lowest stimulation level) when I call her to me? How often should I use the collar? Everytime initially?

I will try breaking up the training session into multiple short ones. Before she begins playing, during playtime, and after playtime. I will see how it goes.