Traffic situation should be much better this year with Uber and Lyft out of the horseshoe for pickup. That being said, the week leading up to Christmas is generally pretty busy at LAX. Christmas being on Wednesday this year means most people will probably travel the weekend before... I suspect Thursday 12/19 and Friday 12/20 will start to get crazy and 12/21 Sat and 12/22 Sunday maybe nightmare days.
I would try to get out by 12/19 if I'm OP.