Open the project file in Apple Motion for which you'd like to extend the length of the timeline.
Locate the stopwatch icons in your Motion project. Both stopwatch icons are about the halfway point of the top and bottom of the screen, one on the left side and one on the right side of the work space. The stopwatch icon on the left side indicates the point in time on which your timeline cursor is sitting. The stopwatch icon on the right side indicates the duration of your timeline.
Move your cursor above the box directly to the right of the stopwatch icon on the right side of your workspace. This box has a number inside it that indicates the number of frames your project covers.
Click and hold your mouse above the box that indicates duration in your project file. By dragging your mouse left and right, you can change the duration of the timeline. Moving your mouse left will shorten the timeline; moving your mouse right will lengthen the timeline.
Drag your mouse to the right to extend your timeline until the number in the box indicates the length of the timeline you'd like your project to be.