Timed Entry to Paris Museums?

not sure what his book is saying, but the Orsay, specifically, doesn't require a timed reservation. PMP addresses:
https://www.parismuseumpass.fr/t-en/r%C3%89servation/cr%C3%89neaux-horaires

Orsay has a dedicated line for museum pass holders, no advanced reservation required.
The Louvre and Versailles both require advanced reservations even with the museum pass.

For the museums for which advance, timed-entry reservations are compulsory, even if using the Museum Pass, you are required to have reservation. It's the only way they can try and manage any sort of crowd control. Please refer to this helpful section of the Paris Museum Pass website for the list of museums which require a reservation (not all of them do):

https://www.parismuseumpass.fr/t-en/rÉservation/crÉneaux-horaires

The Museum Pass, itself, has changed a lot since April 2019 especially with the advent of timed reservations. Are you sure this is a good deal for you? There is only one entry per museum now as opposed to previously.

IF it is a good deal for your specific situation, I'll also add that although they are sold in 2/4/6 day increments they are actually now 48/96/144 hours SO you can actually get 3/5/7 days worth of entries out of them. For instance if you have a 6-day pass and enter your first museum at Noon on day 1, then you could enter your last museum at 11A on Day 7 and still be within the 144 hour window.

According to the Orsay website, they do require timed reservations.

"Holders of a Paris Museum Pass or of a ticket purchased from a third-party vendor do not need a time slot reservation."
https://billetterie.musee-orsay.fr/en-GB/products?famille=1933737738230400130

Nope, no reservation needed for the Orsay with the Museum Pass. This is on the ticketing page about. 2/3rds of the way down:

https://billetterie.musee-orsay.fr/en-GB/products?famille=1933737738230400130

"Holders of a Paris Museum Pass or of a ticket purchased from a third-party vendor do not need a time slot reservation."

Oops, skunklet1771, you were quicker than I was but at least we found the same info!

I guess I was too specific in suggesting the Musee d'Orsay. My question really is "Can you avoid making a time reservation at certain museums that recommend a timed reservation, by just showing up with your Museum Pass. Will they left you in if there is space available, or they that strict? "

Your question is - can you show up at a museum that REQUIRES a reservation and just hope for the best?
you can try.

The Musee D’Orsay is now one of those museums in Europe which is so popular, long lines frequently form by 10 am. To be able to skip-the-line is great. Just keep in mind that if you get there at opening time, you will find you can actually enjoy the art in a less crowded and more peaceful environment— something I find optimal for experiencing one of the world’s great museums.

"I guess I was too specific in suggesting the Musee d'Orsay. My question really is "Can you avoid making a time reservation at certain museums that recommend a timed reservation, by just showing up with your Museum Pass. Will they left you in if there is space available, or they that strict? ""

If you are asking about other museums under this umbrella...then it will depend on the museum. For the Louvre, no. Last April I went twice, having timed reservations both days. On both days there were big signs up at the entrance to the queues saying they were sold out for the day. No tickets available at all. Still there were people coming up to the line monitors asking where to buy tickets. The monitor would point to the sign. The people would say Sold OUT???

For a smaller museum this tactic might be entirely possible and was how it was done when you last visited before summer of 2019. At that time the museum pass changed drastically by allowing only one visit per museum to combat the practice by big Asian tour groups of using it serially for multiple groups.

you could also try going the day before, just to get a reservation for the next day

I was just reading a rant on Facebook from somebody who didn’t like to be tied to times and then got upset that they spent several hours every day standing in lines because they didn’t book an entry time . You’re trading flexibility for a lots of time.

Personally? I wouldn't risk it. I'm guessing that flexing for one tourist would upset the others who played by the rules, and that sort of thing can get out of hand if word starts getting around. "Well, other people said that you let THEM in without a reservation!" Nope, having to argue with tourists wanting special privileges would NOT be fun, and sort of defeats the crowd-control purpose.

Nobody especially likes to have to reserve in advance but most-visited attractions all over Europe have had to adopt the system. Heck, we're having to do it for some of the museums in Washington DC we'll be visiting in April/May.

Also traveling to Paris last week of March. Read fine print of timed ticket for d'Orsay. If you miss your time, the ticket is still good for the rest of the day. Even with a museum pass, you will need timed entry for Louvre and highly recommended for d'Orsay. I plan on booking Louvre at 11 on a Thursday and d'Orsay at 3 that afternoon. This is my fourth trip to Paris (always at the end of March before airfares jump in April). Lots of school tours and mobs of Asian tourist groups (not knocking them, it's just that if you're stuck behind them in a museum, you won't see anything, as they are afraid of being separated from their tour leader!) Times have changed. I've been to all of the small museums, too.

Of course, this depends on the museum. No line at the Musee Guimet or the Quay Branly in January (we had a timed entry at one but not the other. Didn't need it at either). The Carnavalet Museum won't even take a timed reservation for a PMP holder (also no line in January). There are plenty of less popular museums on the PMP where you can absolutely show up without a timed reservation and be fine. But not the Louvre and probably not the D'Orsay.

There are plenty of less popular museums on the PMP where you can
absolutely show up without a timed reservation and be fine. But not
the Louvre and probably not the D'Orsay.

Again, the Orsay doesn't require a timed-entry reservation with the Museum Pass. See the two posts earlier in this thread with text copied from their website.