I'm driving to Vegas for memorial day weekend (staying there Friday night and Saturday night) and was wondering when you guys would suggest leaving (I'm not from the LA area). Some of my friends suggest leaving at around 5 AM on Friday morning to avoid traffic but I've been looking online and people say that as long as you leave before 3 PM on Friday you should be fine. I was planning on leaving at around 11 AM. I'll be leaving from Westwood.
Vegas bound traffic starts early on a 3-day weekend. If you leave @ 11 plan on a ~5 hour drive. This is the absolute latest I'd leave. If you leave @ 5am, you will get there quicker, but you'll be waiting hours to check in to your hotel.
If you are staying at a Vegas hotel, does it offer early check in? If so, I like to leave L.A. early as to make it to Vegas by noon or 1pm.
Most of the traffic you may encounter will be in the L.A. basin. You could take the 405 N to the 101/134/210 and hit the 15 from there. Otherwise you will be going down the 10 E through downtown to the 60 (my preference) or remain on the 10 E to the 15 N.
I wouldn't leave at 3 before a major holiday weekend. This drive is normally a 4 hour affair assuming moderate traffic in L.A. and no major accidents on the 15 North, leaving early minimizes potential delays and gives you time to check in a relax a little at the pool from the drive. May make for a more enjoyable experience.