Thanks for the additional details, northsourcing.

QuickBooks Desktop automatically calculates the digits you entered in the QUANTITY and PRICE/RATE columns. Remember that the Quantity column also calculates the number of hours. 

Instead of adding columns, you can create an Overtime item. You can set it up as Service or Non-inventory type.

1. Click Lists at the top menu and select Item List.
2. Right-click on any of the items and and select New.
3. Select Service or Non-inventory in the TYPE field.
4. Enter the name of the overtime item.
5. Enter the Rate, Tax Code, and the Account if necessary.
6. Click OK.

Every time you create an invoice or other sales transactions, you can add the overtime item manually. You can also ask your accountant if they have another option to achieve what you want.

Let me know if you need additional assistance about the steps. Have a great day!