My alma mater had one like that. Worse, it had
operating hours in general: it was closed at night, too.
It was the Student Information System that we used to register for classes, pay tuition, update our contact information, etc. So it was a pretty important system.
One day, I asked someone who would know. I was told that it was because SIS ran on an old mainframe that couldn't read and write the disk at the same time. So it made all changes in memory during the operating hours, and then it shut down and wrote out the disk at night.
(also, our username for SIS was our full SSN... and the password they assigned to us was the last four digits of our SSN)