It simply says they can use the feature that often. It never says that it’s an at-will action/feature. “At-will” isn’t even a game term in 5e as far as I’m aware.

Possibly the most ignored sentence in the PHB, even by Wotc themselves:

Their skin tones cover the full range of human coloration, but also include various shades of red.

Or it replaces it with an even more complex inventory tracking game of how can I fit all of this in a 4x4x4 feet space. I’m sure some mathematicians would have a field day.

Yeah, that is so frustrating as somebody who plays a character that requires short rests. Our sorcerer throws out her 5th level spells every encounter and I have 2 spell slots as a warlock…

The original Yeeti