System Role Membership Attestation

I have a question with system role membership attestation. 

I have a requirement that every 12 months after an Employee is added to a certain system role (PersonHasESet).

I've  added a condition to only retrieve memberships (PersonHasESet) from the particular system role. 

I want to set the schedule to "Daily" so it checks every day, but my question is how do I scope attestation, so it recertification occurs every 12 months from the point the system role membership was granted.

Thank you