iOS: MIDI clock and note timing via Core MIDI or machine time?

I’m planning to make my own iOS sequencer app. That’s going to take a lot of preparation before I can even start. I have a very preliminary n00b question so that I don’t take the completely wrong approach when the time comes. Does Core MIDI somehow manage low level clock and timing issues, or is it up to the developer to use the machine time (in nanoseconds ffs) to calculate things out so that BPM and PPQ work in the musically desired way?

It looks to me like Core MIDI does all the stuff you want to do MIDI-wise, but you have to have your own scheduler that “manually” calls Core MIDI routines in musical time. I want to make sure whether or not Core MIDI doesn’t has some functionality that automagically makes rhythmic timing easy.