I’m not a philosopher; but on a technical basis, lots of OS work just fine on embedded systems that don’t provide a real-time time-of-day clock and only have time-since-booted to work on - but I don’t believe either are strictly necessary for a preemptive OS to work just fine provided the CPU itself supports millisecond-scale interrupts for the thread scheduler to work. But that made me wonder if it matters at all that a process’ time quanta have a wall-clock-based unit of quanta (e.g. people say Windows uses a 16ms quanta for foreground processes and something else (possibly variable?) for background processes. I imagine a scheduler could use a simple cpu clock cycle counter instead. Even though clock cycles themselves are also variable. And if it’s variable then it cannot be used as a clock.
…so who needs a clock? Turns out you don’t need one. I suppose that means we should just live in the present. Take each day… hour… second as it comes.
…or something. I dunno. As I said, I’m not a philosopher.
Electronics these days measure time passing by counting oscillations of e.g. a quartz crystal. They know e.g. 16000000 oscillations is 1 second +- 0.001%. They don't know when 4pm is.