Parking at Rocky Branch shouldn't be a problem. Parking at Pinkham might be an issue.
It's 3.7 to the Rocky branch shelter site, moderate, steady climb which levels out and goes back down hill towards the end. I left the parking lot early afternoon and had enough sun light to get to the site. BTW, once to the Isolation trail, the shelter site is to the left a little ways. No sign that it's there, but the trail passes right in front of the remains. Only space for a couple of tents, a strip of flat ground - old road bed looks like. The actual shelter site is rough. I did this trip early September last year, so had a little more evening daylight.
It's another 2.7 to the Davis/Isolation junction, but that is for the most part an easy level hike. There were several campsites along the stream there too. I would say a mid morning start would get you to the Davis path without any trouble, or at least to one of the sites along the way. I remember one was pretty inviting.
I suppose one could make it a loop back to Pinkham without a whole lot of effort. Just the climb up to Boot Spur. Heck, you only gain 1000 feet in 1.6 miles. The Glen boulder trail would be the easiest way to get back down.
Looks like it will be reasonably warm and dry until Monday night. I'm looking at a Sunday/Monday overnight hike somewhere myself. Won't say where