The link for the specific schedule tends to be uncooperative most of the time, but here's the main YARTS link: http://yarts.com/routes-schedules/
Roll over the routes and schedules tab at the top of the page and select Mammoth Lakes- Hwy 120/395. When it opens, click again on Yosemite Valley to Mammoth Lakes. All times and stops are there....and it's cheaper than the hiker's shuttle too.
Holler if you need anything else. Have a great trip!