To Obtain an S rating based on pure speed, quickly eliminate the former Mbele soldier in the plantation, then rush to the mine. If you destroy the local anti-air radar, you create a new landing zone, which you can use to extract the children in record time. Alternatively, once you have the child-compatible Fulton upgrade, you can extract them from outside the tunnel, then leave the area by Fulton recovering one of the containers while standing on it.