When at the Hyatt Regency, have the concierge print you a driving map showing a good, non-freeway route from Century City to the airport / rental car return area. Taking such a route (Overland to National to Sepulveda, maybe?) will allow you to bypass the freeways that will resemble car parks at that hour, as well as making it easy to refuel the gasoline (petrol) tank before returning the car.