I can tell you that when I trained 3 times a week in the beginning with grippers it was way too much. I never really felt like I was exhausted in my muscles just started to have pain in my fingers.
There are some great programs out there, one on the grip board that has 1 heavy day, 1 volume day and 1 day that is some other type of grip training. I started using the BB crush and BB flexion and extension as a building block working back into grippers.
What we think, or what we know, or what we believe, is in the end, of little consequence. The only thing of consequence is what we do. -John Ruskin