Hi,
To choose the working days, you just check the boxes next to each day of the week. If it is checked, it's a working day. If it is unchecked, it's not a working day.
The dates that you actually choose are all for holidays, which you can effectively use to make the other 25 (or so) days into non-working days if they are not on a recurring basis such as Saturdays or Sundays.
The calendar feature isn't all that configurable, so personally I think it's reasonable to use an Excel Spreadsheet (or some other table type of input) as an input for a process, and that spreadsheet would contain either (1) days the process should work OR (2) days the process should not work.
Dave
Dave Morris, 3Ci at Southern Company