We're flying into LHR from IAD with a connecting flight onto Rome. If our gate is in 5C when we arrive, do we have to go back to 5A to go through security again and then find our gate to Rome? Or; are we able to clear security in each of the satellite terminals?

How long does it normally take when you get off the plane, to make it to and clear security and be on your way? We arrive at approximately 0630 on a Saturday morning.