Vilages of Western France

Candes-Saint-Martin is charming, but very small. An hour or 2 would be sufficient. Chinon is much larger, and is worth at least half a day.

It really depends on you and how thoroughly you like to visit. But...
Rochefort-en-Terre is a couple of hours, while the Abbeye Royale de Fontevraud is about the same once you buy tickets and wait for a guided tour. It's too hard to say about St. Malo and Chinon because it depends on your interests.

Some highly subjective comments:
1. We thought Beuvron-en-Auge was overrated, crowded like DisneyWorld, and artificially "quaint,". (We found nearby Cambremer to be very charming, authentic-appearing, and home to a restaurant with one of our more memorable meals in Normandy: Au p'tit Normand. An hour or so in either village will be sufficient (without a meal); neither is very large. Just driving without much of an itinerary in the area (or following the well-marked cider or cheese routes) will be pleasant and perhaps produce some surprises. (You won't be far from Honfleur -- not on your list, but worthy of consideration.)
2. MSM: near the top of our list, not to be missed if possible. Research the strategies for crowd-avoidance (or at least minimizing). We drove to/from MSM in one day from Bayeux, quite easily (with an early start from Bayeux.) Others will recommend spending a night in MSM, and that's probably good advice as it apparently gets pleasantly quiet in the evenings.

St Malo deserves the better part of a day, maybe you'll be staying there or near-by. Chinon at least 1/2 day. Fontrevaud Abbey about 2 hrs. MSM a 1/2 day or an overnight stay.

Hard to say how much time to spend in them because we don't know your interests. Have you been to Normandy, Brittany and the Loire before? I've been to five of these villages, and I'll assume you haven't visited before:

St Malo: I'd overnight here if possible. Walk the walls and then stroll the beaches, depending on the tides. Read "All the Light We Cannot See" before going.

MSM: Arrive late in the afternoon, stay overnight on the island, and get off by 10 a.m. before the hordes arrive.

Rochefort-en-Terre: Good for two hours, including a nice lunch at a creperie

Abbaye Royale de Fontevraud: Half a day max to explore the abbey and the village

Chinon: The town is charming but the chateau is basically a ruin that they tarted up with high-tech video screens. I'd overnight here but not spend a lot of time in the village (head for the vineyards instead).

Thank you all for the advice!
Our plan as of now is to leave Paris for Rouen, spend a few hours there, rent a car and spend the night at a B&B in Saint-Samson-de-la-Roque that we found. Drive down to Beuvron-en-Auge then to Pointe du Hoc all before spending the night in Dinan. Using Dinan as our base we'd visit MSM, St Malo and St Suliac over the next 2 days. Leaving Dinan we'd visit Moncontour and Rochefort-en-Terre on our way to Chinon to spend the night. Visit Montsoreau, Candes-Saint-Martin and Abbaye Royale de Fontevraud before heading to Amboise to visit the chateaus.

Thoughts?

March is way out of season so in general most places will have not so much visitors. The places are not so big, to my opinion a few hours is enough for a visit, unless you can visit a museum or so.

If you drive from Rouen to Samson-de-la-Roque along the A13 you can make a detour along le Vieux-Port at the left bank of the Seine (take exit 26 direction Pont de Brotonne) and Marais-Verneir. You can follow different routes to SdlR, your B&B can certainly give you more info about the most interesting one. Lovely places and countryside, from nearby Pointe de la Roque lovely view over the Seine Valley.

Saint-Suliac is worth a visit for sure, there are more lovely spots along the banks of river/estuary Rance. I liked the view over the river in Mordreuc with the castle at the other bank.

About St Suliac and Moncontour, 2 hours should be enough, a bit more if you expect to walk in the nature around, or if you are interested in having a look at the work of local craftsmen.
You could allow for 3 hours as well, if you add Dinan to your list in Brittany. And there would be so many other interesting towns in the surrounding area, in the inlands or along the coast!