Isso é abordado no Guia de Xanathar para Tudo , página 144:
Some magic items can be used a limited number of times but are recharged by the arrival of dawn. What if you’re on a plane of existence that lacks anything resembling dawn? The DM should choose a time every 24 hours when such magic items recharge on that plane of existence.
Even on a world that experiences dawn each day, the DM is free to choose a different time — perhaps noon, sunset, or midnight — when certain magic items recharge.