Unfortunately, you may not track a certain amount of hours each month for an annual license in a single credential because only one time frame may be associated with each credential, however, there are a few options to consider:
1. You may build one annual and one monthly credential where assignments can apply to both.
2. You may build an annual credential and assign out the monthly assignments with start and due dates for that month. To make it more organized, name the topics by month so that the users know which assignments they are supposed to do each month.