I have one day in Yosemite in early May, but it's a full day - can start early and end as late as I want. What's your recommendation to see as much as possible? I'm looking at going up four mile trail, then across the Panorama trail and down the falls trail to Happy Isles and catching the shuttle back. Is this the best option to see as much as possible (panoramas, falls, quiet trails, beautiful creeks, etc.)?

The Four Mile trail is currently closed partway up the trail at Union Point, which keeps you from hiking up to Glacier Point (and continuing across to the Panorama Trail). It may be open in early may (others on the forum will have a better read on that). You probably have read that this year was a big'n for snow, impacting a fair amount of higher elevation trails.
- Here you can see the historical opening dates: https://www.nps.gov/yose/planyourvisit/seasonal.htm
- Here you can see the current status: https://www.nps.gov/yose/planyourvisit/conditions.htm

You should still have options on North Rim (Yosemite Falls is the obvious longer hike), as well as the Mist/JMT that you mentioned, up the Pohono (which is pretty hefty), and others depending on your comfort/equipment for snow. Let us know what your thinking!

I can't comment on snow/trail conditions this year, but....

Mist trail-Nevada Fall-LYV-Merced Lake and back is in
the 25-30 mile ballpark, but not as tough as it sounds.
Lots of sights and sounds, and worth every step.

If the FMT is open then, that route is definitely worth taking. Note that the shuttle doesn't go to the trailhead for FMT - best bet is to park near the trailhead, then take the shuttle from HI to yosemite lodge and cross back over the meadow to the trailhead. Or park in the day use lot (is that still open now) or at the HI parking lot and walk ~2 miles (flat) to the FMT trailhead.

If FMT is closed, consider doing an out-and-back along the upper yosemite falls trail, continuing from the falls either west (to Eagle Peak and El Capitan) or east (to North Dome) before returning. Or taking Mist/JMT and going as far as you can in Little YV before returning.

Just fyi...

Good suggestions from the other peeps... but expect VERY slow going beyond
Bunnell and lots of snow still in Echo Valley (if you get that far after going up
Bunnell Switchers (you should do advanced search on that)
Anywho... yeah, Eagle Peak Meadow... will be DE-lish.

Here was my idea... and then I said... best not say

Anyway,
Up Mist all way to Nevada... down JMT (if Ice Cut open) or down Mist back up
Clark Pt. connector... down JMT... then over to Mirror Lake loop... past rockslide
then around and up Snow Creek to views galore... turn around by first long
switchback... back down.... rest of Mirror Lake loop... over to The Majestic...
then over to Lower Yose Falls... then up Yose Falls to Columbia Pt... and around
to Upper Falls view.. then back down and u dun.

Probably about 8K elevation... about 20 miles... doable

Have fun

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Long-time Yosemite naturalist Carl Sharsmith was once asked what he would do if he only had a day to see Yosemite. "Madam," he replied, "I'd sit by the Merced River and cry."
If I had only one day -
You could hike the entire day or...
Early morning at Degnans...couple of Sausage-Degs...watch the falls.
Morning bus to El Cap Meadow...see the climbers and walk some Valley trails - Bridalveil - back along the Merced ...soak up the Valley.
Afternoon - bus to Happy Isles - Top of Vernal/(Nevada?), but do see the Mist.
Pizza and Cadillac Margaritas at the Curry Deck.
A fine Yosemite day!