Actually, you may as well create the fire when you need it, instead of moving it in at a certain time. Just use the following lines:
fire = "catfireXXX" createvehicle [fire position]
fire inflame true
where "catfireXXX" is the type of cat effect (found by placing a fire in a map, saving it, and then looking in the mission.sqm under "vehicle = XXX").