It's been a few years since I did it and that was by car. As britenbsas says it's around 6 hours by coach and I assume they'll be rest stops along the way. It'll be interesting to hear if they supply food and drink along the way.

The journey was interesting for me due to the different landscapes you go through.....if you're not that keen on geography it might be boring. The route we took sees you passing the wine and fruit growing area then you get into very arid countryside where they have found some dinosaurs remains...(some of the biggest in the world were found in the area). Interesting rock formations as well. You may see the Lanin volcano in the distance as you enter the more fertile area where the Andes start. It all depends on the route they take but there aren't that many choices. Doing it in darkness will almost certainly be boring so I would definitely get a morning flight down there.

As I said I found it a nice road trip you might not of course.