I thought I alluded to that with my comment about them all feeling pretty nasty by the time they got home. I was merely saying that it would be possible, not necessarily advising them to actually do it. That is a decision that would have to be carefully examined and considered. I know 18 year old drivers who are perfectly capable of driving point-to-point on Interstate highways safely, but I also know some that scare me to death.

Yes, 4 days would be a much better decision, no doubt. 600 miles a day is doable by one experienced driver, two drivers would make it a lot easier. That's 12 hours on the road, and in June this can all be done in daylight.