You have 15-17 minutes
After having read the available albeit limited information so far,
the following relies on memory so those of you with charts may have more accurate distances.
1. They were in contact with Shanghai Control when the fire was detected.
2. This means they were past FIR Boundary waypoint LAMEN. LAMEN is 150 nm from ZSPD ( Shanghai - Pudong )
3. Even if they were exactly at LAMEN they were 210 nm ( via airways) to RKPC (Jeju)
4. Therefore it seems they did not divert to the nearest airport - no idea of WX/ NOTAMS at the relevant airports.
5. They reported control problems at 7600' i.e. Less than 5 mins to landing in an emergency. I haven't flown the B744 in years but I remember some control cables run along the roof of the cargo compartment.
6. I acknowledge that emergency diversions into mainland China are not an attractive proposition and that Jeju was an online and probably maintenance base for OZ but IF(!) the above assumptions are true then once again all these cargo fire incidents say that you must have the airplane on the ground or water in 15-17 mins..
7. Not trying to to be a Monday morning quarter back and second guess the Captain as I wasn't there. Condolences to the families