You can use send/receive or OSC for sending any data to M4L instruments.

But there will be some (unpredictable) latency depending on the amount of data.

For low traffic I've measured latency/jitter in the order of 10 milliseconds.

No that is not what I mean...

If I have notes recorded in arrangement view, can I access a

notes duration with M4L. I can then use that duration to control

the shape of my sound in my M4L instrument.

Is this possible?

You can only access the notes of a clip (in session view).

Using 'select_all_notes' and 'get_selected_notes' should give you a list of all notes and their parameters, including duration.