how to start physics on a different time then the frame rendering ?.

I would like to start rendering on a different time (later) as my rigid body physical simulation (should start earlier).
How do i set those different ?

That should be simple enough. You can select the frame range for your physics simulation in its cache tab, and the range for your render in your time line. So, for example, you could set your physics cache for frames 0-250, and your render frames from 100-250.