Stick with your original plan. You arrive way too late to try to attempt to pick up a rental car and drive for 1.5 hours to Ontario. It will take you about 30 minutes on average to go from the terminal curb side to a rental car lot (10~15 minute wait time, 15~20 drive time) so if your flight arrives on time at 11:30 pm, you won't be able to pick up a car until well past midnight (20 minutes to taxi and park at the gate + 30 minutes for deplane and luggage + 10 minutes wait for shuttle bus + 15 minutes drive time = 75 minutes minimum time from touch down to rental car desk). This assumes you are arriving on a domestic flight... If you are arriving on an international flight, you won't get to the rental car lot until 2 AM.
On Friday morning, I would take it easy and eat a breakfast at the hotel. There is no point in leaving early. Some hotel has rental car counter so you may not even have to go back to the airport to catch the rental car shuttle. Pick up your car around 10 AM and head out towards Vegas. You will avoid most of the monring rush hour traffic. Take the I-105 to I-605 to CA-60 to I-15. This route avoids Downtown LA and the heavy truck traffic on I-10. Plus if you have 2 or more people in the car, you can use the carpool lane, which should be pretty speedy during mid day.
Last edited by bzcat; Apr 17, 2012 at 4:46 pm