Now, I saw this movie with five girls who thought it was great, so your mileage may vary....but I thought it was just so-so. The big problem I had was with the two main characters, both of which I didn't think were likeable. I mean, I wasn't rooting for them at the end because they had both turned me off so much.
As for Robin Williams, I like him, but he didn't have much to do in this movie. He played the minister, who was really pretty creepy (bugging their apartment, having a mini-me of about 12 years old). If you missed it in theaters, I wouldn't even bother giving it a whirl on DVD.
Doing it in 48 hours would be good as stretching things out are getting overdone. It would still give them chance to make little side trips. "Kids, while we waited for five minutes, we talked about that ten day trip to blahblahblah..and a goat!