I'm going with everyone else on this one, usually we wouldn't be bothered about driving that distance but landing at 6.30pm it's going to be pretty late be time you get on the road, I would say around 8pm.
The car rental places are all off site and you have to get a bus so time will quickly go, if you were landing around 3pm I would say to go for it.
I know most people on the board have got out of the airport quickly, we landed there about 18 months ago and it took ages to get through immigration and to the bags I think it was like 2 and half hours until we got in the car.
If you stayed over near the airport then you will probably be awake early and can get on the road.