Unanet offers a robust leave accrual functionality that allows for a user's accrual of leave time (PTO/vacation/sick) based on the passage of time or years of service.
The following must be set up regarding Accruals:
1. The Accrual Plan in Admin > Setup > Accrual Plans.
2. The Person Association to the Accrual plan.
a. This can be done in the Person Profile, or otherwise en masse for multiple users via the Person Accrual Association Import.
3. The Accrual post schedule in Admin > Schedule, if you wish for the accruals to post automatically. The easiest way to schedule this to set it to "Daily." This does not mean it will post Daily, only that it will look daily to see if there is anything to post.
If hours off are accrued based on the number of hours worked by a user, then a custom solution can be written to accommodate these needs.
The following resource documents this approach: KC - Quick Topic - Best Practice if you accrue leave by actual hours worked.