Next week my husband and I fly from the East coast to New Zealand. We will have an almost 8 hour layover at LAX. We arrive at LAX around noon. What might we do with that time? I'd love to see the Getty museum, would that be too far to go? Or maybe a nice restaurant in a pretty area?
Do we really need to get back to the airport THREE hours before the flight?

If it is a Sat or Sun you should have no problem getting to the Getty and back. Car rental might be cheaper than a taxi, it's a 15 to 30 minute drive depending on traffic. So allow an hour to get there and three hours for the Getty. There is a nice Restaurant and a good, more casual garden cafe.

The problem would be getting back to the airport in 5pm weekday traffic. You'd have to allow probably a full hour on weekdays, and have an alternate route planned should the freeway get clogged. Not difficult with some pre-planning, and no you don't need to be back 3 hours in advance. International recommendation is 2 hours these days, and your bags are already checked through so 1.5 hours should be more than enough for you.