1620. Obviously
Great Builder's words made the experts widen their eyes. The fact that Heaven and Earth needed to accumulate energy every once in a while was quite surprising, but his lines contained something far more interesting.
'What in the world are the Cities in the sky?' Noah shouted in his mind, even if the name already described a lot.
"You must consider that Heaven and Earth deplete most of their power in the constant expansion," Great Builder explained after noticing the surprised faces. "These lands only get the leftovers of their full might. Conquering planes and filling them with "Breath" is the real deal."
His explanation only made the experts more surprised. The structure of the planes and Heaven and Earth's projects had always been a vague topic in the cultivation world, but Great Builder seemed to know everything.