In the Scheduler there is an option to reschedule late planned day jobs. If this option is checked DMS will revert to the number of operation hours that are required and try to schedule the operation to complete sooner (ignoring the planned days setting). If not checked the planned days setting is always taken into consideration.

Note: if the operation hours against the Resources capacity exceeds the planned days than the operation will schedule out longer than the planned days setting. For example, if your Planned Days is set to 2 and you have 24 hours of runtime against an 8 hour/day resource the operations duration will be at least 3 days not 2.