The leave rules for full-time and part-time employees are the same as they will be covered by the Factory Act/Shop & Establishment Act and the relevant Standing Orders.
While the leaves are the same, the applicability will be in line with the number of hours they work.
So if he gets 1 day for every 20 days worked, in the case of a full-time employee, he gets a full day leave, and the part-timer gets leave for the hours he normally works. In effect, he also gets the full day as he was only required to work those many hours.