Misunderstood Midnight Maintenance Windows

by Chris Josephes

Every once in awhile I will have maintenance windows that need to start at Midnight. When announcements are made, there's always going to be one person out there that gets the day wrong. If I say the system will be unavailable Wednesday at Midnight, I will be asked if I mean Tuesday night leading into Wednesday morning, or Wednesday night leading into Thursday morning.

Technically, Midnight is the beginning of a new day. If you're used to military time, it's easier to understand, since you're starting over at 0000. But most people have always used Midnight in the context of a late evening, as in, I'm going to stay up until Midnight; so it's pretty common to accidentally associate it with the previous day.

To overcome confusion, we announce all Midnight maintenance windows as having a start time of 12:01 AM. It's close enough to Midnight, and for some reason, everybody seems to understand it. Sure, Midnight is ambiguous, but 12:01 on a Wednesday is clearly early understood as Wednesday morning. I'm not going to complain about a one minute compromise if it means avoiding ten minutes of writing emails to clarify the schedule.


2007-08-15 06:44:22
It is for this reason that we generally schedule maintenance at 11pm or 1am (or later), depending on the time zone of the target systems.

Personally, I've never really understood why midnight is so hard but apparently it is, sigh. I guess in the same way that many people seem to confuse 12am with 12pm.

2007-08-18 20:42:59
You've got the right approach (12:01 AM) 'cause Midnight is ambiguous (and 12am and 12pm doubly so).


2007-08-22 00:39:48
This is only an ambiguity for idiots, and since there's no shortage of idiots in the world, this probably makes for a good policy.
Mark Leighton Fisher
2007-08-22 10:11:28
Insurance policies (the ones I have seen) always start at 12:01am or 12:01pm just to avoid this kind of confusion. (Interesting that the NIST thinks so too.)