"8AM to 12 PM" think you mean 12 AM unless you go to bed at lunch :)
> hour is represented by two digits from [00] to [24]. The representation of the hour by [24] is only allowed to indicate the end of a calendar day
And Page 17:
> NOTE 1 Midnight will normally be represented as [00:00] or [24:00].
> NOTE 2 The end of one calendar day [24:00] coincides with [00:00] at the start of the next calendar day, e.g. [24:00] on 12 April 1985 is the same as [00:00] on 13 April 1985. If there is no association with a date or a time interval both a) and b) represent the same local time in the 24-hour timekeeping system.
> NOTE 3 The choice of representation a) or b) will depend upon any association with a date, or a time interval. Representations where [hh] has the value [24] are only preferred to represent the end of a time interval in accordance with 4.4 or recurring time interval in accordance with 4.5
24:00 has no duration, it's only an instant in time. The same could be said about 11:34 of course, as long as you assume 11:34 to mean 11:34:00.0000000000000000000000 and not the interval from 11:34 to just before 11:35.