The 40/40 takes around 45mins of mob killing. Did it with a full group some got it done after 30mins and the last one got it around the 50min mark.
We had worldquests in legion with worse drop rates - WORLD QUESTS. Not sure why so many in this thread are trolling.
If you cant figure out where to do it, because you managed to ignore even the small zones in BfA you can just join a group: