I was wondering how long is too long to preferment a sponge for a loaf? My recipe recommends 12-14 hours, but I let it go for 24? Could this ruin my loaf? Thanks!
At this point, you have nothing to lose so go ahead and finish it.
If it's overfermented to a point where it has completely collapsed and lost structure, yes, of course.
and the size of the preferment and temperatures involved. If a large portion of the dough is prefermented and overfermented it will definitely affect the dough. Temperature should also be considered. A cold preferment might be fine.