Is Zakat obligatory on the amount saved monthly and cumulatively with the company, which is paid after three years unless the employee violates the conditions?

The money allocated by the company as an incentive for an outstanding employee is not considered part of the wage, and the employee does not own it until after three years. Therefore, there is no Zakat due on it for the past period because the employee did not own it. However, if the money is part of the wage and its entitlement depends on specific conditions, this is a فساد عقد إجارة (a voidable lease/employment contract) due to uncertainty (جهالة). In this case, the worker is entitled to an 'اجرة المثل' (a customary wage/fair market value wage), and he must pay Zakat on what he has received from it if it reaches the نصاب (minimum threshold for Zakat) and a حول (full lunar year) has passed. As for what he has not yet received, he pays Zakat on it upon its receipt for the past years. If what he has received exceeds the customary wage, he must return the excess to the company, and there is no Zakat due on him for that excess amount.