I did that last year at Bridalveil Creek. 3rd week of July, I drove up there about 11:00 a.m. on a Sunday morning and half of the sites were vacant. I think it filled by about mid-afternoon.
Sundays or early in the week, showing up by noon or 1 p.m. should do the trick.
Mike G.
Liberty is meaningless where the right to utter one's thoughts and opinions has ceased to exist. That, of all rights, is the dread of tyrants. --Frederick Douglass
photo: Yosemite Valley view from Taft Point