The word day is ambiguous, but calling it 24 hours is not perfect either. A 24 hour period can include leap seconds, meaning it can be one second longer or shor

The word day is ambiguous, but calling it 24 hours is not perfect either. A 24 hour period can include leap seconds, meaning it can be one second longer or shorter than 24 * 60 * 60 seconds. (At least that's how ISO8601 defines time periods: 11pm-12am is a one hour period even if leap seconds cause the last minute to have 59 or 61 seconds)