Is this a realistic itinerary?

So I'm planning on hiking the JMT in either July or September (August isn't possible with my work) and I can realistically only take about 2 and a half weeks off at one time. I'm coming from the UK, so from looking at a few resources online, the best option for me seemed to be fly to into San Francisco, and make my way to Happy Isles via Merced and YARTS HWY 140, which from looking at the schedules seems to be possible in one calendar day if I have a flight early enough. I'd hopefully be able to stay somewhere there and then depart the next morning.

I used /u/jordanvincent 's interactive planner to build a draft 14 day itinerary that would vary between about 12 and 20 miles per day, with between 2-5k ft in elevation change. There's 1 rest day on day 7 at the MTR with a resupply. After this I'd get a shuttle to Lone Pine and take the ESTA 395 North to Reno to fly home.

Does this seem like a realistic plan, or am I being a bit ambitious, and would July or September have the best conditions for moving fast (I'm also aware July permits are already going, so September may be better)? I've done a few somewhat similar treks in the UK covering similar daily distances and elevation changes, however the longest trip I've done is 5 days and never at quite the same altitude. I'm also planning a few approximately week long warm up trips throughout the year so hopefully my legs shouldn't be too fresh.