Creating an Effectivity 
You create an effectivity to specify a time period during which a rule should be effective while engine execution. By assigning effectivity to a rule, you can control the period of rule execution.
Procedure
Locate the Project Resources node (Where is the Project Resources node?) and double-click the node.
In the Project Resources editor that appears, choose the Effectivities tab.
In the effectivities editor, choose the Add button.
In the dialog box that appears, enter a valid name for the effectivity in the relevant field.
Select all or the relevant check boxes as follows:
Effective Date Period: Select this check box to set the start date for rule execution.
End on: Select this checkbox to set the end date for rule execution
Weekly Reccurrence: Select this checkbox to select the days during which the rule must be effective.
Effective Time Period for Each Day: Select this checkbox to set the start time and end time for rule execution.
Discrete Dates : Select this checkbox to select those dates during which the rule must be effective or not effective apart from the time period already selected.
In the is Effective column, click on the default value and choose the alternative value (true or false) in the drop down menu.
Based on your selections you should see the summary of the effectivity set in the Preview section.
Choose OK when you are done.
In the Effectivities editor, you should see the effectivity name and the details about the effectivity under the Effectivity Condition column.