The ‘Period’ field in the assignment rule defines the period for which entity records (work items) will be assigned to users. It has the following options -
Daily: The work items will be assigned on a daily basis.
Weekly: The work items will be assigned on weekly basis.
Monthly: The work items will be assigned on monthly basis.
Overall: Since there is no definite period as such, work items will be assigned as per the standard assignment rule. When this option is selected, ‘Open Work Item Statuses’ field will be made available to be populated.