Many magic items in Pathfinder give the user some benefit a number of times per day or for a number of rounds per day. To pick a random example, the Boots of Teleportation state
Any character wearing this footwear may teleport three times per day, exactly as if he had cast the spell of the same name.
Is it ever stated just when used charges are regained? For example, I could imagine it happening at midnight, or after an 8-hour rest.
Two closely related questions:
If a magic item changes hands, are the charges used by the previous owner still gone? Or could five different people each use the boots to teleport three times per day?
If you have multiple copies of the same item, can you swap them out to get more uses per day?