Baldur’s Gate 3: Spells & Cantrips Explained - DualShockers
To recover your spell slots for the day, simply take a long rest. Getting the full benefits of a long rest will give you all of your spell slots back, while a partial long rest will only restore half of your spell slots.
Is there a RAW way to allow the PCs to recover only some ...
Level 1 Spell Slots → 38% * If you have max Spell Slots (4), you will recover 1 slot at first Short Rest, and 2 more slots at second Short Rest.
Short rests every ten minutes. What breaks?
One thing to stress about this interpretation is that it leads to a question of whether a warlock spell slot created in this way could recover on a short rest or not.
Warlock 5e: DnD 5th Edition Class Guide - RPGBOT
Equally as important though, the rod also gives you the ability to regain a spell slot as an action which, funnily enough, almost doubles your available spellcasting slots per every short rest.