Subscription Crystal Boxes are shipped on the 30th of each month via Royal Mail Tracked (unless 1st class is selected). They usually take 2-3 business days to arrive. If your box is reported missing, it's often at your local sorting office. If you sign up on or after the 20th, you'll receive your first box the following month. For example, sign up on November 19th to receive December's box, but sign up on November 21st to receive January's box.
When you sign up, your first payment is for your first box. Each payment corresponds to one box, and boxes are delivered according to the schedule at the time of sign-up.