tenpo ko (toki pona for “elemental time”) was invented by marzka of marzka.cafe and Joop Kiefte. The idea is to split up the 24 hour clock into 4 constant six hour blocks relative to UTC. This creates a simple universal time that is easy to remember and compare across timezones.
So for me, I know roughly that my mornings are water and my afternoons are earth. If it's half past fire, I should start getting ready for bed. And I generally sleep through air.