I just did this drive on Thursday. I took the 101 to the I-5. I hit maybe 10-15 minutes of traffic approaching downtown L.A., and another 5-10 minutes approaching the El Toro Y in OC, but no big deal. I got to the outskirts of L.A. around 11 AM, so I missed both the morning and afternoon heavy commute volume. That's really critical, in my experience. You really want to time it to get through downtown L.A. by 1 PM at the latest, if at all possible.