hi, there's room for more on this one, but you may find these interesting

• Why does a new day start in the middle of the night? - featuring /u/itsallfolklore

• Why do days begin at midnight?

• What event 00:00 (or 24:00) time points to and why?

Thanks to /u/Searocksandtrees for the links. If you have additional questions, please let me know.