Bird:

doing it 48 hrs before, as opposed to 2 days wouldn't be a nightmare at all, since the upgrades are done via computer, it would be very easy to program.

Continental did in fact use 48 hrs and 72 days, rather than 2 and 3 calendar days, several years ago. It worked just fine.

Since I am a night-owl I prefer the midnight rule, since I'm usually awake anyway.