To add Work Calendar Exceptions for Work Calendar:

Login with a user with administrator privileges and click on Administration option under the user profile
Under the Project Management section, click on Work Calendars.
Navigate to the Exceptions tab.
Click Add.
From the For drop-down, select the Work Calendar for whom you want to enter an exception.
In the Summary box, type the details of your event/exception.
From the Impacts Scheduling drop-down list select an option - Working / Non working.
From the date picker select a date. You can create the event for a whole day or for a specific time (un-check the All Day checkbox).
From the Repeat tab, select an appropriate option.
Click Submit. The exception is added.

To delete Work Calendar Exceptions

Login with a user with administrator privileges and click on Administration option under the user profile.
Under the Project Management section, click on Work Calendars.
Navigate to the Exceptions tab.
For the exception you wish to delete, click on the delete icon.
Confirm the deletion by click on Yes. The exception is deleted.

Adding or Deleting work calendar exceptions would impact the task schedule. For example, if you make a working day as Non-working, then the task's finish date will shift to the next available date. Similarly, if you make a Non-working day as working, the task will be re-scheduled to finish earlier.

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