Just to keep the ball rolling, if you're not around to sign the banner and you reserved a spot. You have an hour from the time the person before you uploads the file.
After an hour of the uploaders post edit time, if the next person isn't online or hasn't indicated that they're signing or uploading, then they'll be skipped and the next person after them is free to sign.
Don't feel bad if you get skipped though just be sure to try again later when you know you'll be around to sign it more quickly otherwise people have to wait and it's not fair.