Your mileage may vary. On August 19th we flew into LA at 11:15 am, and because of slow luggage output we caught the Alamo bus at 12pm. By 12:30pm we were on our way to SD. Yes, I used the Car pool lanes as much as I could. 5 does not have car pool lanes the whole way down to SD from the LA airport.
It took us exactly two hours to reach the 28th street exit, exit 13. Long drive, but not much traffic. We then drove from SW SD at 6:30pm on Wednesday, Agust 21. We ht a lot of traffic once reaching the LA city limits, and pulled into the Sheraton Uiniversal two and three fourth hours later. The last 45 minutes were crazy wall to wall cars and trucks.
On Friday, August 23, we left the Highland and Hollywood garage in Hollywood at 1pm and pulled into the Grand Californian in DLR at 2:30pm. The traffic all the way was heavy, stop and go every so many miles. Yet, on Thursday, August 29, we left the Grand C at 10:15am, and was at the Alamo rental at 11am. No real traffic until 3 or so exits before the airport one.
I always use the car pool lanes when I can. They usually do not have much traffic on them. The only exit I could get off using a car pool exit was for Disneyland. The other exits I could not. I did pick up the other highways I needed from the car pool lanesmost of the time.
Safe travels. My kids are used to 4 lane one way highways. In CA , we saw 5 and 6 and maybe even more lanes each way. Some of the highways were really wide. I don't mind the driving though.