Engine fire on ground after RTO in low Vis:Recall items and discharge BOTH bottles WITHOUT waiting 30 secs.
I believe the 30 secs in the air is in case you discharge one and the fire signal stops you may keep the second bottle in case the fire comes back....on the ground if the fire comes back after both bottles discharged..evacuate.
If still sign of fire :Parking Brake set,Speed brake stow,Call for flaps 40 then QRH checklist.
When time comes to call for evacuation, check fire situation one last time(may have extinguished by then).
Fo will advise tower of evacuation and approximate position for fire rescue.
Capt becomes PF if stop call is made hence he performs recall items.