I asked this question on Stack Overflow and it was closed as off-topic. I'll ask it here hoping it will do better.
This might sound silly, but bear with me. I've been working a lot with intervals and dates lately. One question that bothers me: is a day really 24 hours long? I'm interested by the answer both from a theoretical and from a practical point of view.
Let's take today for example, the day started on 13 Dec 2012 00:00:00 and according to (all) date-time implementations it will end on 14 Dec 2012 00:00:00. This is correct and the difference between the two dates is a complete 24 hours.
The problem with this is that the end date is perceived as "tomorrow". Most people thinking that a day starts on 00:00:00 and ends on 23:59:59.
So the question is: is today a closed interval at the start, and opened at the end, like [start..end), with the end being very very close to 14 Dec 2012 00:00:00 (so not really a complete 24 hours)? Or is it actually closed at both ends with a full 24 hours between them?