A majority of my maximum effort (i.e.,~7s of effort with ~2 minutes of rest) training is done on the hangboard. By choosing the hangboard, I progress (i.e., add weight every time) with the grips (e.g., open hand, 1/2 crimp, and full crimp) I most commonly use.
What should I do during the seemly too long resting periods? Zone out to my ipod. Look at climbing nuggets. Those are okay options.
It is better to use the resting time as training time. Climb Strong suggests lower body static stretching while waiting to crank. In my experience, my hangs are negatively impacted by lower body static stretching. Instead, I work to improve my dynamic range of motion. I improve one of my limiters (mobility) and not impact my finger training. I save the static stretching for the end of the session.