In AM11, on a task schedule, holidays cannot be added as an exclusion where the schedule is set to operate on hours, minutes or seconds. For example, it is not possible to create "run every hour except on holidays" while the interval selector is set to hours. The desired schedule can still be achieved by setting the interval to something other than hours, minutes or seconds temporarily (e.g. set to days) then add the holidays exclusion, then set the interval back to hours, minutes or seconds.