Yes, it's a full 24 hours, but a library doesn't use 24:00:00 to represent the last hour, it's 23:59:59. Once it hits 24:00, it rolls over to 00:00:00.

Hence my initial error of answering 23.

It's not valid, but I don't edit out erronous answers because I believe all data should be preserved, no matter how dumb it makes one look.