What time should we leave in order to be able to get from LA to SF in time to make our 4:45 flight?

Where in LA? It is a HUGE area.

But in general -- that is a CRAZY idea. It is about a 6.5 or 7 hour drive w/o any traffic or holdups. You'd have to be at SFO before 2PM to give you time to return the rental car.

I'm willing to assume you have good reasons for wanting to drive from LA to SFO on the day of your flight. I agree with janisj that you should plan to get there about 2 PM. Google Maps says the drive time from downtown LA on I-5 is about 6 1/2 hours. You should add time for early morning traffic in the LA area, and put in an allowance to account where you are starting from. And add a little time for pit stops and a stop for lunch. If it were me, I would probably try to hit the road between 6 and 6:30AM.

Here's the problem: We got our air with a complicated mix of ff miles, companion fares, etc. The ff miles didn't allow us an open jaw flight or so it seemed, so we're flying into SF and out even though our flight stops in LA in and out. I think my husband is still trying to investigate the possibility of getting on in LA since that's where we think we'll be at the end of trip. From the looks of it, it sounds like we better leave the previous day from LA and stop somewhere that we didn't see on the way down.
Feel free to tell me what I should have done re: ff miles and open jaw flights, so I do it right the next time.

I know that using United miles to go to Asia next year, we were permitted a stopover OR an open jaw, but not both (we opted for the latter, and will make our way to Hong Kong ourselves for the return flight).

I'd consider leaving LA after rush hour the night before, drive up 5 (the ugly way, but who cares at night), and just drive until you feel like stopping --- maybe you'll make it all the way to SFO to sleep.

You might be able to fly JetBlue or Southwest from the LA area to SFO fairly cheaply--worth checking into.

I definitely agree w/ SAB. Drop the car at LAX -- unless there is a HUGE drop off fee. Then fly LAX to SFO either late the night before or early the next morning. Much easier than driving all the way.

I agree too - I just assumed flying was not in the mix.

Or - there are several other LA area airports depending on exactly where you will be at the time. Burbank, Ontario, Orange County, Long Beach, even San Diego . . . .

All have flights to SFO.