Billing officially start the second your create a droplet. They may do a preauthorize on the card when you enter it but that will come off in a few days.

Bills are totaled for the month based on total hours droplet(s) has been created. (Yes this includes power off state) Then card is then charged the 1st of following month.

I haven't seen any in awhile but they used to give coupon codes for $10 credit. Card still required! Check around the net you may find one.