The last two times that I went to So.Cal, we flew in and out of vegas. I like to stop and get InNOut, (in Bakersfield? or is it Barstow?) or ChickFilA in Corona, nummy!
We weren't even combining the trip with anything else, we simply could save over $400 by flying in and out of vegas for our last trip. Money well spent at DLR, as far as I was concerned.
We were always going opposite traffic, but I have to say, I would do whatever I could possibly think of to not be traveling that stretch on a Sunday going West! My first trip, we were on the road heading back to Vegas on Sunday, and saw a back up as early as 11am when we were just over the mountains outside riverside! No kidding! That meant that people had to be up and out of Vegas around 7 ish at the latest? The bottle neck (as in barely inching along parking lot) continued all the way into Vegas. It never let up.
The last time I went, we were once again heading back on a Sunday. This time it was later at night. We were about mid-way at 9pm. There wasn't a portion of the trip that we didn't see a long line of cars. When we reached Vegas at about 11pm, it was still backed up all the way.
The drive toward Vegas on Friday evening is reputed to be almost as bad. It's slightly better, as some people choose to go out on Thursday night, during the day on Friday (for long weekends) or on Sat. early morning.
If I could make a recommendation, if it would work for you, spend the earlier part of the week with your family/friends, then come back to Vegas to head out. OR, find something to do in Vegas on Sunday and then head out Vegas on Monday at some point.
Honestly, you're short 4-4.5 hour venture could easily turn into a 10 hour nightmare, and at the beginning of your trip, too!