When the Divine Condor brought Yeung Gor to Dook Goo Kau Bai's Tomb of Swords near Seung Yeung Fortress, Yeung Gor estimated that Dook Goo Kau Bai must have lived around seventy years before his own time after examining the artifacts that DGKB left behind.
Yeung Gor was not a historian or an archaeologist, so he was just giving his best guess based on his observations, but I think he was about fifty years off.
At the time that Yeung Gor visited the Tomb of Swords, around forty years had passed since the beginning of LOCH (e.g. the birth of Gwok Jing). If you add another thirty years (going backward) to that, we're in the era when Central Divinity Wong Chung Yeung was young and doing his thing in wulin.
Remember, however, that none of the elder Greats had ever encountered or even heard of Dook Goo Kau Bai, while Dook Goo Kau Bai was said to have gained his reputation by having dueled and defeated all the martial arts experts of the time...which did *not* include Central Divinity Wong Chung Yeung, Ancient Tomb Sect Founder Lam Chiu Ying, and the other Greats. In fact, by the time Wong Chung Yeung and the other Greats emerged in wulin, Dook Goo Kau Bai was unknown and forgotten. Since Wong Chung Yeung and the Greats first became renowned during the ten to twenty years before LOCH began, then Dook Goo Kau Bai's time of dominance must have been closer to the final years of the Northern Sung Dynasty...e.g. the same time period of Wong Seung (the creator of the 9 Yum Jen Ging, whom some have theorized was one of the martial arts experts whom DGKB defeated), which is around seventy to eighty years before the beginning of LOCH and therefore, at least 110-120 years before Yeung Gor visited the Tomb of Swords.