If you miss the 72 hour deadline, you won't get kicked out. You'll become ineligible for the grand prize (merit badge + access to awesome groups that can help you through NaNoWriMo) but you'll still be able to participate, use the calendar, and finish the challenge.

Just remember you're not required to finish each assignment before you have to log it. You're just required to spend 15 minutes working on it. So, if you work 15 minutes on your outline, but don't complete it because life gets in the way, no stress. Log the assignment as completed and get back to it when you have time later. It also doesn't have to be presented neatly on Writing.Com for everyone to see. If your character profile is scribbled onto the back of a scrap of paper, it counts! If you write out your antagonist's background story in the same notebook as your school notes during lunch, you get to count it as done. Just find a place to store all these loose pages, scrap papers and scribbled on napkins.

I'm terrible with time management too, but just remember, this is not supposed to be a stressful challenge. It's supposed to help you by getting you to think about all the aspects of your character. Is it helpful to have a complete profile for each character written? Yes! But so long as you have the basics and you've thought about the rest, you're already more prepared than you were without Prep.