In "getting there" you said "... at Road's End - you can take either the side of the creek....the right side ( when looking east ) being shorter, but in the sun...The left side is a little longer, but may offer better shade." I was there 10 days ago. Looking east, the left (north) side looking east that is about 1/2 mile shorter and sunnier. The right side (south) is a little nicer, cooler, and longer - you have to go a little west from Muir rock, from the south parking lot, and cross a bridge for the south side route.
It might be a time of day or time of year thing then. I specifically remember baking in the sun heading out on the south side and enjoying a cool hike in the shade on the north side when coming out. As far as the length, it was hard to tell while doing it - but, I got that info from the ranger. It felt long both ways to me ... on the way out from the heat, on the way back from being dead tired :)