Dragon Quest Builders 2 takes place after Dragon Quest II
It seems that Dragon Quest Builders 2 will be taking place not too long after the actual Dragon Quest 2 game that came out on NES featuring an order that revolves around the antagonists of those games. Down below is a more in-depth description by Gematsu:
“In Dragon Quest II, the corrupt cleric Hargon (who planned to destroy the world by sacrificing his own life to summon the God of Destruction) and the God of Destruction Malroth were defeated by the descendants of the heroes, and peace visited the land, but a religious order that inherited Hargon’s intentions appeared with the intention of eradicating the Builders.
The peace that came after Hargon’s death collapsed with the rise of the “Hargon Order,” whose goal is to destroy the world. The Hargon Order spearheads the destruction of towns and castles all over the world. The earth falls into ruin, and there are little remains left of peoples’ lives.”