From reading this thread, it seems like match/challenge requests get granted within a business day.

We're planning to do a AS MVP -> UA PS match, but it looks like our travel plans *might* mean that our return leg of the itinerary that should meet the challenge requirements will likely be a couple of days outside the 90 day window (i.e. ~2nd April - I'll aim to submit the challenge on Dec 31st, as our MVP expires the day - unless FTers suggest against it. Not sure if this is cutting it too fine..?)

Does anyone know if UA has exercised some kind of discretion in such situations?

I'd prefer just to stick with UA if it seems likely that we can get some kind of discretionary credit for the anticipated scenario above, if not, would we be able to book with UA and then switch credit to A3 at the gate?

Thanks in advance