That's the incongruity, for me. Time turners don't just seem like the solution to the troll problem, or any particular problem, which you'd have to come up with as the problem arises. They seem like the solution to practically all problems. The particular way they're presented, they'd require you to use them as soon as you identify the probable casus belli, but before you learn of too many specifics.

So, not something you'd have to think of ad hoc, but an optimal problem solver you'd always keep close at hand (replacing your wand, even) for whenever your spidey sense tingles. Sorry for invoking such an unrealistic concept.

Probably something that should've been left out of HPMOR entirely, just because of its lack of balanceability.