Switch to an in-universe time length.
‘This spell recharges at the next dawn, as long you have fleemed the scrabinator.’
‘This spell can be recharged by having a really good meal with your closest friends.’
‘To recharge this spell, you must sacrifice a male hare on an alter to your god under the full moon.’
This provides a sub-task that the caster is motivated to reach for, which helps with RP and moving the story along.
This is how most magic works in Unknown Armies, by the way. That game is fantastic and just drips with flavor and insight (2nd edition anyway. I haven’t read 3rd)
If your book mage wants to charge up, he has to go find some rare valuable books and add them to his collection. If the chaos mage wants a charge, she has to start taking some risks. You can do some crazy things with a major charge, but getting one is probably work. Or win Russian roulette if you’re a chaos mage.
In practice it can be difficult with a large group where everyone has their own obsession. It provides good down time options and plot hooks, though.
