The way Mit Jeut See Tai told the story to Chow Chi Yerk in HSDS, one gets the impression that Gwok Jing and Wong Yung hurriedly had the Heaven Sword and Dragon Sabre constructed just days if not hours before they died and Seung Yeung Fortress fell to the Mongols. That doesn't seem likely, however. To devise such a complex plan, gather the necessary materials (they used Dook Goo Kau Bai/Yeung Gor's Heavy Iron Sword as a basis, but added additional materials to it), transcribe the texts of the 9 Yum Jen Ging and Mo Muk War Tactics Manual (in packages small enough to be contained in the hollow of the two weapons, at least in the first two editions of HSDS), find a blacksmith capable of forging such weapons, etc...sounds like it would take years of planning and preparation. My impression is that the Gwok couple (probably more Wong Yung) had the foresight to know that Seung Yeung would eventually fall, and initiated the Heaven Sword and Dragon Sabre project years before the fortress city fell. Perhaps they had prepared the weapons for up to a decade before the final siege.