Turn on the LENGTH button.
Change the part number that appears in the display to the length you want using the + or - buttons. You can also type in a value. Push record. This will tack on time to the end of the part or make the end of the part shorter based on the value entered.
To add or remove time from the top of the part use the PAGE UP / PAGE DOWN buttons to go to the menu that says "CHANGES PART TOP". Change the length and push record.