Thanks Dave and Micheal.
I will try to count some frames then.
Michael, if I drag with the ALT tab and drops it on a layer,will it not then replace the hole layer, I am cutting out pieces in different moments, so I guees I have to find out what frame I cut it out and remove that from my AE comp, after I render out that part, and then import the new one in as it own layer and match them up somehow.