Absence plan using vested reference period

Summary

Looking for expert experience with using similar plans

Content

Hi,

I am looking for experience on how others handled a similar vacation accrual requirement: 

Accrual: The company has a vacation reference period from May 1 to April 30.   Employees must complete a full year within the reference period in order to qualify for the vacation plan.  So if I start in February 2018, I would accrue vacation starting on Feb 2018 but I am not allow to take that vacation until May 1 2019.  So I accrue but am vested  until I have completed 1 full reference year.   

The vacation that I accrue (current year) is not available for use until the next reference period.   So vacation days earned from May 1 to April 30 2019 --- this balance needs to be transferred and Available for use starting on May 1, 2019 for those that have completed their reference year.   The entire balance is front end loaded on May 1, 2019