There are 2 dates for Plesk license that was ordered in the online store:
1) Update date.
All Plesk licenses has renewal date set every month. License in being updated in Plesk each month, this is done automatically and does not require any actions from Plesk Administrator. Please refer to the article #213375429
Monthly and Yearly Lease Licenses are being updated in Plesk each month.
2) Billing date.
Billing date fully depends on the billing cycle you chose during the purchase.
Monthly Lease Licenses are paid every month.
Yearly Lease Licenses are paid once in a year.