When the instructions say "15 minutes" they mean 15 minutes. Are you welcome to do more? Of course. BUT YOU GET CREDIT AS SOON AS YOU HIT THE 15 MINUTE MARK.

Don't psych yourself out on the first day because you can't come up with a premise you like, or one at all. You have a whole month to work the kinks out of your story. If you spent fifteen minutes trying, you get credit for the assignment. End of discussion.

Cheers,
Michelle