You may be slightly overthinking this. LA traffic is unbearable, and unpredictable, every day of the year. As you said, among the few strategic decisions you could make would be to travel opposite rush hour.
However, I considered, on my similar trip, The Getty Villa, to be "on the way to LAX". So I think I chose 10 or 11AM for my Villa ticket, and continued to the airport in the afternoon.
I was glad to see the Villa, but the original Getty Museum has a much larger and more important art collection and grounds. In the end, you're looking at an interesting reproduction, not a /real/ Roman Villa (the collection of objects in the display cases indoors, aside.) It would be a shame if you chose your hotel purely for seeing the Getty Villa. For example, although it is "far" (from a freeway traffic point of view!) away, I also went to see the Norton Simon Museum and the Huntington Library and Gardens, both in Pasadena. Unless you have a degree in Archaeology, either of those two museums is much more important and rewarding than the Getty Villa. I also went to LACMA after arriving at LAX on the way in. Unbelievably, I got a two-hour spot on the street, which I went "back to" once during my museum visit. I think I stayed in or near Calabasas, in a low-end Hilton-derived property.