Meteor Galaxy Developers edition question

Hey guys, I am having a little bit of a problem. I just got my galaxy developers invite and am getting ready to sign up but there is a problem…Im broke until the end of the week and I need to add a credit card in order to sign up. Does it charge you even when signing up or is it only when a container is opened? The reason Im asking is I dont wanna use my card since it doesnt have money on it for a few days but I dont wanna lose my invite since its expiring in a few days. So I guess the question is does it just check to see if there is money on the card and not charge it or does it charge automatically for a single container whether its being used or not?