No problem to do that, even at my slow 65 yo pace and gimpy knee
in 2015 we camped at SBL. There are about 4-5 tent sites on the south rock wall overlooking the lake and two sites on the north shore, where we camped. Both are just off the trail and very easy to miss. Many people camp below SBL in a stand of trees not on the water and of course further south and lower and longer for the day you propose. If you stay there you are adding 30 min or so.
Once over the pass, there are three main lakes: #1 at foot of Crabtree Pass, #2 has a beach, #3 has outlet off to the right leading down to Crabtree Meadows. Following the drainage down, look for a horse tie-up area and find the old trail that saves you time and distance by not going straight over to PCT but angles through the woods toward the Ranger station and JMT.
times:
710am left SBL -over Crabtree pass and arrived overlooking the lake with the beach at 300 pm. We camped in a very skimpy never-used-before-make-do sparse site between lakes #2 and #3 far off the trail.
next day 710am to 125pm second set of tarns above Guitar.
way too much time boring time in camp. if you add up those ACTUAL hiking times over the 2 days it is 14'05". Sure, it can be done in one day.
we saved a bit of time after using the old horse trail toward the PCT by cutting across Crabtree Meadow off trail and arriving near the Ranger Hut and JMT. But going up to second set of tarns above Guitar added 20 min. So all -in- all you could do it in under 14 hrs with more normal hiking speed than mine.
I had done the route before, so if this is your first time, you will need some route finding and awe-time time added in.
I should add that we saw a Scout troop go in one day from below SBL over Crabtree over Discovery Pinnacle(not your route) to Whitney and return all in one day. Amazing .
see trip report from 2014 and maps (times listed above were 2015 trip without side trip to Langley and camping at SBL as you plan to do)
http://www.whitneyzone.com/wz/ubbthreads...d_nor#Post39834 
