Which day of the week to visit D Day Beaches?

Monday is better than Sunday and Saturday for tourist attractions in general

I would opt for Monday. Check car rental locations, because once you are outside of the large cities, many of the locations are closed on Sunday. We always take the train from Paris to Caen and rent our car there.

The Memorial Museum of the Battle of Normandy in Bayeux closes between 12:30 PM and 2 PM during the off-season. Its website indicates that it is open 7 days a week, as is the Airborne Museum in St-Mere-Eglise. The Airborne Museum does not take a mid-day break.

The best day will be one where it is not raining and the wind isn't too high. As for any other consideration, I don't know of any.

I would not be concerned about crowds. The area is massive - 50 miles from east to west. We were there at the end of May. The only place that was a bit crowded was the Airborne museum but anything outside will not be a problem. Using a live guide will greatly enhance your understanding of the sites.

You will wish you had spent more than just a few hours there...

I can't remember which days I've been there, but my impression is that Monday will probably be a bit less crowded. Are you only going to be spending one day touring the D-Day historic sites?

Although your husband is a "HUGE WWII history buff", you might still consider using the services of one of the local guides for at least part of your visit, as they're outstanding! They have a lot of information that's not in the history books, as they've toured with veterans of the landings. You'll learn more with an expert guide than be seeing the sites on our own, and (IMO) it will be a much more interesting and memorable visit. If you need suggestions for a few of the guides in the area, post another note here.

Does your one day include driving from and back to Paris? That's about 5 hours of driving round-trip.

With such limited time to see the beaches, that could be a very frustrating day for your WWII history buff husband. You might be better off saving the D Day beaches for a trip when you have more time. Or, consider a small-group tour from Paris. With your husband driving, he/you will have no margin for error. An organized tour could be a more efficient use of your time.

I don't know how often it is offered, but last year I stumbled on information on Overlord Tours' website about a full-day tour designed for people staying in Paris. I believe the deal was that the tour pick-up point was at Caen RR station a bit later in the morning than the usual departures from Bayeux (which is farther from Paris than Caen). It would be possible to hop on a train in Paris that morning (early, admittedly) and make that tour. That's the only way I'd even consider trying to see the D-Day beaches from Paris, and it would really be better to head up to Bayeux late in the day, on the day before the tour, and spend the night there.

Overlord's full-day tours were priced at about 100 euros per person last year.

I also recommend going with a guide. You can take it all in instead of focusing on driving and directions and parking. Even if your husband knows as much as the guide he may find it restful to not have to do all the explaining. We did two days with Dale Booth and covered only the American sites, so go with the intention of coming back to see it thoroughly.