If not all of the products in your subscription are delivered on the same day, each additional item or package will be proratedly billed for the current month.
The products will begin to be billed on a monthly basis starting with the following invoice.
Let's imagine, for illustration purposes, that you ordered two packages on July 19, 2021. If the order is delivered in parts, with some things arriving on July 24 and the remainder on July 29, 2021, the products that arrive on July 24 will be invoiced for 30 days (the full subscription cycle), while the items that arrive on July 29 will be invoiced for 25 days (pro-rated according to the subscription cycle).