There is a video that I just made in my profile of a Go Pro timelapse. It's nothing special, but I learned a few things making it (now I won't repeat those mistakes when something I really want to get comes up).
I used a 2 second time interval, but if you were looking to save battery I imagine a slower one would do just as well (especially if it's of something slow like snow accumulations). Make sure you practice today with something trivial so that you are ready to go for "the show" tomorrow. I had my camera freeze on me on my first attempt and only got 40 pics out of that attempt.
The time lapse I did only lasted an hour I think, and you can see some pretty significant changes in that amount of time. However it was my 8GB card that filled up before my battery filled since I was taking a pic every 2 seconds. Therefore I think it's fair to say that you should get the full extent of the battery used if you slow it down to 5 seconds. Of course if you can simply swap your battery and pop in a new card after a while to double the time of your time lapse if you are still awake!
Thanks for the code too, your my favorite person right now.