So not only did they break into the most heavily guarded prison ever, not only did they break out the[*] most dangerous criminal known to be still alive, not only did they get away with it all to boot, but they did it BEFORE LUNCH!

[*] (assuming that MoR!Voldemort already killed Grindelwald)

(OK, I know, they had plenty of time in their own personal timelines to eat lunch. And they didn't finish until after lunchtime. But still.)

Thank you, that clears up my confusion.

I am afraid that I am too used to intelligent fictional characters having supernatural powers of planning and foresight. I suppose it is much easier to have readers be impressed with intelligence if smart characters are simply omniscient rather than acting rationally at all points. Therefore, if you were to be writing Quirrel with maximum intelligence, he simply MUST have planned it all at the earliest possible moment. It didn't occur to me that they could just be making the best of a bad situation, since that doesn't maximize the illusion of cleverness. He's a very smart human; he's not L/Light.

I'll try not to be so hasty to make assumptions in the future and scan for any unspoken assumptions that are coloring my view when reading MoR. On further reflection, that's a good general life lesson too.