HostedScan charges per target scanned per month. You can add unlimited targets to your account without charge. Only when you scan a particular target, does one of your account's target scanning licenses get used.
Once scanned, that target may be scanned with all the scanners, an unlimited number of times, in that billing month without using any additional licenses. At the end of the billing month, all target licenses reset, and may be applied to other targets in your account.
For example, if the account is paying for 5 target licenses, but has 10 targets in the account. All 5 licenses get used in the billing month when a scan is performed on one of the 10 targets. At the end of the month, those 5 purchased licenses get reset and may be used to scan the remaining 5 targets in the account the following month.
Licenses reset for both month to month and annual plans, at the end of each billing month. If you have purchased your initial subscription on January 5th, then February 5th, the licenses would reset, regardless of annual or month to month plan.
You can view your Usage details and your billing cycle reset date by visiting the Billing settings in your account.