[sixothree]

Those intervals overlap. Does 00:00-01:00 _actually_ imply 00:00-00:59?

Also you're describing seems to be intervals, not datetime format.

edit: further:

This is directly from the RFC this thread is about:

Date and time expressions indicate an instant in time. Description of time periods, or intervals, is not covered here.

[taylodl]

In practice the intervals don't overlap as they're understood as follows [23:00-24:00) and [00:00-01:00). That is the interval begins precisely at 23:00 or 00:00, but ends as close to the endpoint as your timing resolution allows. This way we don't have to write cumbersome expressions such as 23:00-23:59:59.999.