You can begin your monthly subscription at any time. You can do so by entering the app menu, clicking on monthly subscriptions, select an available garage, pressing subscribe and confirming. You will be billed a prorated rate for the remainder of the month and billed the on the 1st of the month.
PLEASE NOTE: By confirming your subscription you will be IMMEDIATELY charged and your billing cycle begins. Only subscribe to the monthly service on the day you want to use the service for the first time.