[AlotOfReading]

The time it takes to put things on a physical bus will depend on your hardware and can be bounded, but this isn't the guarantee you're getting from any RTOS.

The main thing the "RT" in RTOS guarantees is that the OS will return control back to you in a defined amount of time as soon as you're ready to run. You're still responsible for ensuring all of the other system requirements for bounded latency are fulfilled, like hardware that doesn't introduce unbounded latencies the OS can't control (surprisingly difficult with modern HW). Assuming you've done all of that, preempt-rt will give you essentially the same guarantees because of the scheduler work linked.

Yes, AGL = automotive grade Linux.