It's standard to say 12h and expect this to read as 43200?

Sounds like a lousy standard if the correct way to use it is to say "I want to delay by 12 hour seconds". What is even "12 hour seconds"?

Makes sense once you know it.

"Sec" suffix indicates time and implements a default of seconds, where a suffix to the value indicates a change in unit.

It would be like Asking "Memory Allocation(MB)" but accepting "12G" for 12 GB.

In our code at work we have constants like HOUR=3600 and RESTART_TIME_SECS = 6 * HOUR. It makes sense to me. If it doesn't for you, feel free to use something else I guess.

Standard where? I have never seen this before and I’ve been reading *nix configuration files for 20+ years

Standard within systemd (i.e. consistent).