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.

https://linux.die.net/man/2/clock_gettime

   This clock is not affected by discontinuous jumps in the system time (e.g., if the system administrator manually changes the clock), but is affected by the incremental adjustments performed by adjtime(3) and NTP.

   If the adjustment in delta is positive, then the system clock is speeded up by some small percentage (i.e., by adding a small amount of time to the clock value in each second) until the adjustment has been completed. If the adjustment in delta is negative, then the clock is slowed down in a similar fashion.