The Employee Shift Scheduling model supports queries for time worked, e.g.
  • Maximum 160 hours per month.
  • Maximum 40 hours per week.
...
But it's cumbersome/impossible to do the inversion though, e.g.
  • Maximum 30 free Sundays per year
  • Minimum 11 consecutive hours off per day
  • Minimum 2 consecutive days off per week
This is a request to be able to specify rules for "non-working time".