I dunno. How many encounters is the average DM running per rest? If a 1st to 5th level Twilight Cleric gets to shine (yep) for one combat per rest, does it really break anything?
That's not really a good way to judge though.
If I homebrew a class that has the 2nd level feature "can cast meteor swarm.." once per week, is it really ok because it'll only matter 1 encounter per week?