Without having read every response (so, sorry if i am repeating anything):
I went to Bayeux and MSM summer of 2016. I stayed in outside of Bayeux and drove to MSM, with the goal of arriving there around 5p (as suggested by RS). I left my b&b at 9:30 am. Thus, I spent the day driving with no agenda - drove the west/southwest coast of Normandy, stopping in an empty beach town for lunch - taking 5 hours to drive what would take 1.5 if Id gone directly. Arrived at 5p, and everyone was leaving. Parking lots were nearly empty. The abbey was nearly empty. It was amazing. Temps were perfect, vibe was peaceful, sights and views lovely. We walked around the abbey for 2 hours, found some dinner in the little street at the base of the abbey, walked in the mud flats around the abbey (there's a water spigot for hosing off after), and drove back to Bayeux, arriving by 9:30p. A perfectly timed day.
So you could take your time from Dinan. Arrive in MSM in the evening, and still make it to Bayeux for the night.