Gawz, the small bowel series is icky, but shouldn't take too long (although it really depends on how fast your system is). You'll drink 2-3 cups of chalky-tasting barium. They'll start taking x-rays about 15-30 minutes after you drink it, and every 15-30 minutes after that until the barium reaches your colon. For me, it only took the barium about 30 minutes to get into my colon, but that's almost crazy fast. For others it can take up to four hours! So bring a book to pass the time!
After the procedure, you will be crapping "ghost poo" for a few days afterwards. It's white. Creepy-looking. Drink plenty of water and eat lots of high-fiber foods to get that stuff out. Yuck!
As far as the breath test goes, I've never had one of those. From what I've heard, it's a simple test and quick to boot. Good luck with both tests!