going to yosemite for 3 nights at end of may. any suggestions for long walks (3 hours max)with not too much elevation gain.

I'm racking my brains for ideas, but you've put too many restrictions. Either the hikes are in areas that may still be snow-covered (Tuolomne Meadows), have quite a bit of elevation gain (Mist Trail), or will last only an hour at most (base of Yosemite Falls, Mirror "Lake").

If you're sticking to the Valley, your best bet is to wander around. You'll use up three hours oohing and aahing before you know it.

I think you'll just have to walk around the Valley. Check with the park ranger station, they will be able to make suggestions based on what is open.

Mirror Lake would be nice.

Anyplace you will hike 3 hours will have a LOT of elevation gain.

The valley is flat - but it is relatively small and everywhere around it is a long way up. Now, there are shorter hikes everywhere - down in the valley and up on top - but nowhere near 3 hours or 2 hours or even 1.

But as the others say - just strolling around the valley will be awe inspiring.

I would take the shuttle bus to Happy Isles and hike to the bridge below Vernal Falls,about a 3 hour round trip hike.
There will be some elevation gain but you will be rewarded reward you with a memorable view.
Now that the road to Glacier Point is free of snow you could take the 3-hour round trip drive to that viewpoint.
Also, after the 28th of May, you should be able to rent a 2 man rubber raft at Camp Curry and take a ride down the Merced river. Very calm and safe.
The raft trip takes about 3 hours and a bus stakes you back to Camp curry.

I think (no, I'm sure) the OP said 3 hours MAX, meaning shorter hikes are perfectly acceptable.

You can always do Mariposa grove and just not do the whole round trip. Just go as far as you want then turn around. Not much elevation gain there.

I really enjoy walking the trails and paths around the valley - along the river, around meadows, and so forth. Really beautiful views and usually pretty peaceful. You will get a map when you enter the park - the various trails and paths are shown.

There is another hike behind Mirror Lake that is good. Not a lot of elevation change, but a good hike.

thank you, all! some great info and ideas. yes, hikes s/b 3 hours or less (not just 3 hour hikes.) re the hike to the bridge below vernal falls, is there much elevation gain? is this called "mist trail"?