I see 3 tables needed.
1 - employees: holds the employees information
2 - dayoff-types: holds the types of days that the employee can take
3 - days-taken: holds the dates that any employee was off along with the hours and type (from table 2).
This way you would hold your current avaiable vacation time in the employees table, and also the total vacation time accrued. When the employee accrues more time you just need to add to these 2 fields. When the employee takes time you subtract it from the current, and put an entry int the days-taken table.