I recently made a reservation that hasn't yet been ticketed. The confirmation indicates:
We will hold this reservation until midnight Mon., Mar. 1, 2010 in New York/Newark, NJ (EWR - Liberty).


So when is midnight? Is it just after 11:59 Sunday evening or after 11:59 Monday evening? Common usage has it that Monday at 12:00am (which is a "midnight") is between SUnday and Monday. Monday at 2400 would, however, be the midnight between Monday and Tuesday. I suspect that CO means "midnight" to signify the end of a day not the beginning, but an earlier reservation apparently cancelled out at the "midnight" starting the designated day. To avoid confusion, they perhaps should say the reservation will be held to 11:59pm on Monday, March 1st.