Some (not all) shifts can be rescheduled, date and/or time. I.e. ideally the shift is nov 11th, 10am-11am but if that is not possible, it may be rescheduled to nov 12th, anywhere AM or nov 13th 11am-12am. There can be an order of preferred alternatives, this can be a range or an exact slot. All the rules need to be configurable within the dataset, not global (difference groups have different rules). Potentially also the duration of a shift would be somewhat dynamic.