I worked on an embedded system for years that used that exact representation for time. The "fun" part is that it was used to represent real time since an epoch

I worked on an embedded system for years that used that exact representation for time. The "fun" part is that it was used to represent real time since an epoch many years ago, and the field was compulsory. Not only would the values roll over every 12 hours, but the system would have to function for a while before even synchronizing to an external clock. Every so often, somebody asks why the next-gen system has four optional 64-bit time fields, and my eye twitches while I rant about time synchronization for half an hour. Then they ask how to compute the time difference between two independent events, and we're literally inside an XKCD comic.