A matter of time

One of the things that I am having problems with when ever i do any exercise is dealing with how long it should take me to do any one action. As a musician I am trained to do things for a certain amount of time and then move on to the next thing. It is weird to 1. decided for myself how long I am going to do something and 2. make that decision based on how something feels. I thought that maybe I needed to concentrate more and pay more attention to what I was doing, but the more I analyze what I am doing the worse it gets. I'm guessing I need to do the reverse and just react without thinking , but that is really, really hard for me.