Ideally, from my perspective, the clock would be a 32 or 64 bit binary counter I could simply read and/or write directly, with each oscillation of a 1Mhz+ crystal adding one to the count, but even with an RTC it's still far from that, because they are all mostly 1 second resolution! So, at best, they can pump out faster square waves into the atmega328p's rather short timers, but converting that to the virtualized ideal clock equivalent, while remaining highly energy efficient, seems nowhere near as straightforward as it should be.