I concur entirely with Farelli: You need to be your own gauge of what is comfortable versus what is "too much." Having said that, you do NOT need to "dig in," or press "super hard," as that will inhibit your ability to play fluidly.
If it gets to a point where it is "tingling" or "numb," then you are pressing way too hard and need to completely stop the exercise. Sometimes, all you need is 5-10 minutes and a good shake-out in order to be able to continue, and sometimes, you'll need to put everything down until the following day.
GREAT QUESTION!! THANK YOU!!