Four days since they entered the portal, so the others needed to survive for three days before they could return from the game, but of course, three days on Earth more likely thirty days on the other side.
Tang Shaoyang had been experimenting with the existing portal. He and his original team tried to enter the portal once again, hoping to get the real reward but the portal did not allow them to. The notification said they had finished the objective so they could not enter the portal. In other words, once the objective was achieved they could not re-enter the portal even if the portal was still there.
Another was that the people he brought from Arkania Continent were not considered as the player. Meaning they could not join them to finish the game. Kairu, Wen, and the others could not be brought to the sixth portal with him.