Muir is about 30 minutes off the trail but involves some exposed class three. A post a week ago or so had pictures of the Muir climbing route. It was called pictures of MR & Mt. Muir I think.
Russell is more complicated. You would have to descend the North face of Whitney or go down the Mountaineers route to Iceberg lake (loosing about 2000 feet). Both of these would give you access to the Southern face of Russell. After doing Russell you would come down the Mountaineers route to the portal, not easy to do in the dark if you have not been there before (Ebersbacher ledges)
It has been done in under 10 hours by the fastest speed climber. But it could easily take an extra 1 hour to Mt. Muir and an extra 4 hours to Mt. Russell. That might be more then the hours in one day, especially if done from the car. You would have to get a very early start.
