You can only add new working times that do not overlap with any existing working times in the Calendar. 

If you receive an error that says "Start and end time must not overlap with any other existing working times in your profile", this means you are trying to add a new working time that is overlapping with an existing working time already entered in your Calendar. 

To resolve this issue, you need to either delete the existing working time in your Calendar that overlaps with the new time you are trying to add, or you can also edit the existing working time instead of trying to add a new one.