Tough one, part of the experience is the fun. For starter get a hotel the night before. The extra 3 hours of good sleep will pay dividends. Also, be sure the girls have protein drinks and low sugar electrolyte drinks.
Second, is it a big tournament? If it's an okay tourney just let them have fun. If your games are at night and you make them stay down and in all day then I guarantee you they will not have fun. No fun, no future away tournaments or wins. If on the other hand it is a big tourney it's trial and error. Each team and each player are different, and over time you will find what works best for each. Good luck