One very minor correction in your planning. Since Arizona doesn't do Daylight Saving Time, it will actually be on the same time as California and Nevada in May, so you won't actually gain or lose an hour. In the winter, Arizona is an hour ahead.

Bravo on your planning to this point. If you stick with the flight, I think you've got a reasonable plan, but I'll throw another option out there if you'd rather just drive, see Death Valley, and likely save with a round trip airfare.

Days 1-4 in Vegas as you've currently planned.
Day 5 GC, again as planned, stopping at Hoover Dam if you're interested.
Day 6 start driving to the coast, finding a place along the way like Barstow or Bakersfield depending upon what time you leave GC.
Day 7 continue to the Coast and explore the Cambria area.
Day 8 Big Sur/Monterey
Day 9-10 SF
Day 11 Yosemite.
Day 12 Sequoia
Day 13 to Death Valley via Sequoia Monument/Lake Isabella
Day 14 Death Valley
Day 15 Fly back from Vegas.

Its just something to thing about, it also leaves you the option of including Tioga if the pass has opened, which might be a little more likely at the end of your trip, although it could be at the expense of Sequoia.