As to how to implement it - progressing quests would be one way to do it, at least some impactful ones, like the one in the Druid Grove.
I generally dislike timers - what it means is that we have to do resource management with an unknown source. Do you clearly communicate timer for each times quest? That's a bit heavy handed. If you don't then that become a mess as the player doesn't know how they could manage their rests - they get encouraged not to rest, and then they don't use abilities, and then game becomes no fun. If resting is limited, then players have an idea on how they are doing.
Some games that did resting well - Darkest Dungeon and Dark Souls. Not sure though, if there is much to learn here without completely altering a structre of a cRPG. In the end, any punishments added to resting, acts as annoyances rather then solutions. And when adding such limitations, one needs to be careful as to not encourage un-fun game styles - just as unlimited rests encourages un-fun gamestyles.
