We just got back form CSS. Aunt Flo was with us the first two or three days of the trip. We were sweating that worst case scenario possibility for a couple months prior after doing the math.
The simplest situation wound up being the best - "tuck and roll (with it)". Made it a total non-event and I am 100% confident that nobody else was even aware.
True that to what SuzyQ reiterated!