Myr, not Ma. Ma is for dates, not durations.
No. Contrary to what some journals believe, "Ma" is not short for "million years ago". It's the symbol for "megayear": the SI prefix _mega-_ and the almost-SI symbol _a_ for "year" (Latin _annus_).
"Myr" is English, not international, not SI or anywhere near it. That makes it a bad idea.
For dates, you have to spell out "_ Ma ago", or "il y a _ Ma" in French, or "vor _ Ma" in German.
Or the patchwork quilt of terranes that is the Asian-North American corridor...
Quite. That must be a nightmare to reconstruct for pretty much any particular time.