Hmm, hard to say. When I go to any of them, I drive up from San Diego so tend to stay all day and go home after dinner when the traffic might be marginally less heavy!

You could get a good feel for the Getty in maybe 2-3 hours (longer if you eat), the Huntington might take more time because there are the gardens and the art gallery (and tea!). The Reagan library is a couple of hours unless the exhibit is of interest to you. Of course, sitting on the terrace looking at the view would take additional time! None of them are really quick in-and-outs.

there are the gardens and the art gallery

Dont forget the library!

Of course! LOL!

earlier this year my husband and I spent two days in Pasadena and I will third the suggestion of the Huntington Museum and the Simon Norton Museum there.

We were in LA for a late afternoon/evening before taking the Coast Starlight train up to Oakland. With so little time we just explored the area near Union Station where we were staying. We enjoyed seeing the El Pueblo de Los Angeles historic district, and we ate in Chinatown.

I noticed that Fodors has a current article on "ultimate things" to do in LA and am linking to it in case you haven't seen it
https://www.fodors.com/world/north-a...in-los-angeles

Definitely recommend the Getty, LACMA, the La Brea Tar Pits Museum, Peterson Auto Museum, and Huntington Museum and Gardens. All excellent.

The Reagan Presidential Library is about as good as the rest, and I personally find them all quite interesting. Have been to several as of now. A highlight is Air Force One, as is the surrounding countryside. The Nixon Presidential Library is in Yorba Linda to the south of LA, and worth a stop as well.

Trip reports below, one for food, one for attractions:

https://www.fodors.com/community/uni...ences-1411792/

https://www.fodors.com/community/uni...a-car-1402901/

If you go to LACMA and/or the tar pits, you can walk on that Miracle Mile section of Wilshire Blvd and find lots of small ethnic restaurants that are worth a try. The Grove and the Farmer's Market are very close, as well, if you like that sort of thing.

Did you say how many people are traveling and their ages?

The Getty Villa and the Getty Center are very nice, and different than one another. Depends on what you're looking for. We like them both. Each has beautiful grounds, views, and a nice cafe. One needs a reservation that you get on-line.

What else are you interested in seeing and doing?

>>The Nixon Presidential Library is in Yorba Linda to the south of LA, and worth a stop as well. <<

The Nixon Library is fascinating (including the birthplace/boyhood home) and is an easy 12-ish miles detour from Anaheim.

I highly recommend the Huntington Library. I've been going there ever since elementary school as Pasadena schools used to have field trips there.

When places are stated as being in L.A., it doesn't automatically refer to the City of L.A., but to the County of L.A. I'm from Pasadena which is L.A. County. San Marino is adjacent to Pasadena.

I would also include the Norton Simon Museum (Pasadena) and the Gamble House (Pasadena) of which is a 10-minute walk around the corner (on Orange Grove) from the Norton Simon Museum. For nearly 20 years, I lived in the neighborhood of the Gamble House and out-of-town guests and I would walk up to it for the tour and they have all loved it. They also loved the Norton Simon Museum.

http://gamblehouse.org

https://www.nortonsimon.org

If you go to the Norton Simon Museum, then you are also walking distance to Old Town Pasadena as it's on the same street, Colorado Blvd, the Rose Parade route. Yesterday evening, friends and I just walked from Old Town Pasadena and past the Norton Simon Museum to get to the big, Colorado Bridge Party right by the Norton Simon Museum. Central Pasadena is very walkable as I regularly walk all over from home.

Happy Travels!

What about the Griffith Observatory - is that worth going to? Also have read about the tar pits - are those interesting?

Yes and yes.

But I grew up in Los Angeles. I like the old-timey stuff. I'll throw in Olvera Street, Chinatown, and Farmer's Market/the Grove.