Ok... sounds like you need to key the lattice/chess peice at it normal position at frame 1 then you also need another key in between frame 1 to 48 at the same setting as in frame one.

For example key the lattice/chess piece at frame one, than middle mouse drage in the timeline to say frame 40 key it. The key at frame 40 will have the same value at frame one.

Now go to frame 48 and deform the piece and key it. Play back your animation and you should see that the piece dosen't start to deform until frame 40.

If the deformation is to slow or fast just move the key on frame 40 either closer to frame 48 for faster movement or back closer to frame 1 to slow it down

Hope this helps

Kurt