After Effects Remove part of the duration (or a frame) of a layer

In the Timeline panel, set the work area to include only the portion of the layers’ duration to remove: Move the current-time indicator to the time that the work area is to begin, and press B. Move the current-time indicator to the time at which the work area is to end, and press N.
 
Do one of the following:
• Select the layers from which to remove a section.
• Select the Lock switch for layers that you do not want affected by the extraction. Press F2 to deselect all layers.
  
Note:
If no layers are selected, the following step removes the section from all unlocked layers.


Do one of the following:
• To remove the section and leave a gap of the same duration as the removed section, choose Edit > Lift Work Area.
• To remove the section, choose Edit > Extract Work Area. The gap is closed by ripple deletion.