Contract tab does not allow to select the desired holiday for an Employee

Hi
Contract tab does not allow to select the desired holiday for an Employee.
in the contract tab, there is no option to select the working_days_per_week since sat and sun is the default holiday
There should be an option to select the desired holidays(like friday and saturday or only friday)
if am giving working_days_per_week = 5 , there should be an option to set the desired holiday..other than sat and sunday