Supplemental PTO (Compensatory Plan Type) to expire by end of the year

There is requirement to have compensatory plan to end by the year end instead of configured expiry of 12 months.
 Example:- Any supplemental PTO received during any time of year 2024 to expire by 31st December 2025 and Any supplemental PTO received during any time of year 2025 to expire by 31st December 2026.

Tried to configure by increasing 12 months expiry to 24 months but in that case any leave taken in mid-year or towards the end will not expire by last day of the year.

The expiry needs to be visible in front end.

Looking for suggesting and options on how to configure this requirement in this absence plan.