Yes, you can totally do either UBL-Skyblue Lake-UBL or LBL-Skyblue Lake LBL in one day. The hike over to Miter Basin does not take long. You might even be able to tuck in a jaunt up to Iridescent Lake while you are over there. Or scope up the area above Skyblue Lake for a future trip. (I have a hankering to go back myself, to go up and over Crabtree Pass and around to approach Whitney from Crabtree ranger station.)
How good is your route finding? If you take your time it is possible to do all this without ever going beyond class 1 or 2.
The hike out from LBL is about 10 miles, not too difficult some pretty sights but a bit tedious in places. I like doing a loop so I found it worthwhile. There is a connector trail that gets you back to Cottonwood Lakes TH (via the stables). You might think about parking at Cottonwood Pass TH, and walking over to Cottonwood Lakes TH at the start, so that you don't have to do the extra bit at the end.
