Unfortunately, the system does not allow overlapping dayparts for any particular spot.  That being said, the way to accomplish this is not to add an overlapping daypart to a single spot, but rather, add multiple spots each with a specific daypart.

In order to run multiple dayparts on the same days of the week you need to create a new line item for each needed daypart.  Where the first daypart is assigned to the first "spot" and the second daypart is assigned to the second spot.  You can use the Copy Spot function from the Spot Actions menu to duplicate the first spot in its entirety, then just edit the Dayparts for the newly created second spot to meet the needs of the second daypart requirement.

Should you need any help or assistance whatsoever, please feel free to submit a ticket to our support staff via the link at the top of the screen.