Nothing to eat after noon the day before should be sufficient to make sure your small intestine is empty, and really that's all that matters for the capsule endoscopy. Yeah, your colon might still be "full of it," but that won't affect the pillcam going through the small intestine. And once it gets into the colon it's useless, whether or not your colon is empty or full.
Average times for the small intestine to empty into the colon are 2-8 hours after a meal, depending on how much is eaten and how quickly your system works. Once in the colon, things slow down more. But if you don't eat after noon, your small bowel should definitely be empty by the next morning.