To change the duration of a layer in the timeline, what action do you perform?

Changing the duration of a layer in the timeline involves a straightforward action of adjusting the layer's edges directly within the timeline interface. By dragging the edge of the layer, you can either shorten or lengthen its duration, which modifies how long the layer appears in your composition.

This method is intuitive and visually immediate, allowing you to see the effects of your adjustments in real-time. As you drag the edge of the layer inward, you effectively trim it, while dragging the edge outward extends the exposure of the layer, making it last longer.

Utilizing this action simplifies managing layer durations, especially when working with multiple layers or complex timelines, making it a fundamental technique in Adobe After Effects.