Business rules for changes allow you to automate certain actions in changes. For example, you can configure a business rule to ensure that the implementation tasks in a change are only created within the schedule of the change.
To create a business rule,
Go to Setup > Automation > Business Rules and select Change from the drop-down.

Click New Business Rule.
Provide a name and description for the business rule.
Choose a module or sub-entity from the drop-down to which the business rule must apply. This field value cannot be edited later. Available options include:
Approval
Approval Level
Attachment
Downtime
Email responses (from Users)
Note
Task
Worklog
Choose when to execute the business rule - when a change is created, edited, or deleted.
Choose the duration to execute the business rule - anytime, within, or outside the organization's operational hours.
Select Turn on cascade execution if you want successive business rules to be applied on the change. By default, business rules stop executing after one business rule is applied on a change.
Select Enable Rule to maintain the business rule in a usable status. If disabled, the business rule will not be executed.
Specify the condition to apply the business rule.
Apply conditions based on criteria - Define the criteria to apply the business rule by selecting the column, operator, and value. Use the Add icon to define multiple criteria.
Apply conditions using custom functions - Select or create a custom functions to be applied.
Apply no condition - Apply business rule to all changes.
Under Actions,when a rule matches specify to Execute custom actions or Abort process execution.
Click Select Custom Actions and choose the actions to be performed.
Field Update
Custom Function
Click Save.
The following business rule is set to abort task implementations if they fall out of the change schedule.

From the change business rules list view, the following operations are supported

Enable/Disable Business Rule: You can use this to activate or deactivate the business rule you have created.
Delete Business Rule: You can delete business rules using this.
Turn on/off cascade execution: Enable or disable successive applications of multiple business rules to changes.