Hi Yoshiko,
Whilst not a perfect solution, you should be able to use the pan behind tool to help with this.
If the precomp is fully extended to its limits in the timeline (you will see the little black triangles in the top corners of the layer) the pan behind tool won’t do anything.
Therefore, first, you need to trim the in or out point to where you need the layer to start or finish playing (short cut: Alt+[ Alt+] )
Then use the pan behind tool to drag the layer to match that trimmed in or out.
Finally fix the trim on the other end of the footage as needed.
Graham Macfarlane – CGI specialist
Elyarch Ltd – London UK
3D Studio Max | Vray | Pflow | PhoenixFD | After effects | Mocha