PACs get exhausted after each time running away from the ghosts, so they need to refill their energy!
The amount of energy you get depends on how many PACs you have in your team. More PAC means more energy. The energy can be used anytime you want but can be recharged only once per day starting from 00:00 UTC.
You can use the energies when you want, there is no need to play all of them in the same session.