Yes, Sill and Middle Palisade are doable as day hikes depending on your own capabilities.
If you can dayhike Whitney you can probably dayhike Middle P. But, Middle P. requires cross country travel, route finding, extensive 3rd class climbing, a little 4th class and because the snow/glacier melts away from the rock this time of year, it probably will require a couple 5th class moves to get on the upper mountain. It did when I climbed it last Sept. If you have those skills I highly recommend the climb, it was a lot of fun.
Sill is a lot longer, it could be done as a dayhike, but I wouldn’t try it. This time of year you’d need to plan on hiking a lot of it in the dark. I was up it in July. Most likely you’ll need an ice ax and crampons. The route has a very scary 4th class section near the top. If don’t have 5th class skills you probably won’t be able to get past it. The other peaks in the area of Sill are more technical.
Summitpost.org is a great place to check-out the routes.
Hope I didn’t rain on your parade.