I don't know about Calico, it is a little ways off the freeway and not that exciting, in my opinion. If you have the money, you may want to look into a helicopter trip to the GC from Vegas. I think it only takes one day round trip that way. I don't think it is worth all the extra time driving. Save it for a Utah/Arizona trip another time. If you do decide to do it, you should look at the difference in mileage between DLR-GC-LV-DLR and DLR-LV-GC-LV-DLR. I have no idea which is shorter, but to go straight to the GC, I think you'd go through Laughlin, which is just as long a drive, if not longer, from DLR as is Vegas and only somewhat closer to the GC. I could be wrong, though.
Leaving from DLR to Vegas at either time shouldn't be a problem, you should be going against traffic. I would drive over to the 57 , take it up to the 91, over to the 15 and straight up all the way. An alternative would be the 5 to the 10 to the 15, but I think there will be a lot more traffic that way. I like to avoid the 5 whenever possible. Or the 57 to the 10 to the 15. There is an outlet mall in Barstow and another in Primm. The only time not to come back would be Sunday afternoon/night. It can add hours onto your trip. If you are coming back on a Friday, try to avoid hitting the LA area between 4 and 6 pm. All freeways seem to be a mess at that time.
If you have kids, I think the pools at the Mirage, Mandalay Bay and Rio are the best.
Enjoy