How to enter particular off-days for part-time employees

Hi,

I'm looking for an easy solution to enter the specific weekly off-day for part-time employees.
We have employees that are 4 days available in a week, but some have their off-day on wednesday and others on friday.
Is there an easy way to define this?
I was first thinking to solve this through an administrative project so that these days would be taken into account during planning calculation.
But this woul mean a lot of data to enter for each of these employees, is there a better, more straight forward solution for this problem?

Thanks