Absence calculation Belgium

New starting employees do not get Statutory Leave Plan, but a plan for Unpaid leave, because the bring the hours/ days from previous employer

The Statutory Leave Plan can be assigned and hours/ days are calculated but only available as per the 1th of January of the next year.

For existing employees the similar rule is active: the accrued hours / days in a year can only be taken as from the 1th of January of the next year.

So we need a plan where accrued leave is available as per 1th of January of the next year.

Anyone a suggestion how to create such a plan?