Why do you even need to know what the numbers mean in relation to time of day? 99% it is completely irrelevant whether someone is unavailable because they are asleep, at lunch, at dinner, (not) at work,… but just when they are or are not available. Or you just want to communicate an event and that event happens at one time and everyone considering attending it just has to convert it to their own timezone now.
Why do you even need to know what the numbers mean in relation to time of day? 99% it is completely irrelevant whether someone is unavailable because they are asleep, at lunch, at dinner, (not) at work,… but just when they are or are not available. Or you just want to communicate an event and that event happens at one time and everyone considering attending it just has to convert it to their own timezone now.
For travel, for contacting people for social purposes, for a shared global cultural association