The conversation Chu Yunsheng had with the guardian ended in a hurry. The things about the space tunnel, he didn't get to ask everything he wanted to ask. The guardian didn't have time. It seemed to be repeatedly trapped in some kind of intermittent self-locking. Before the conversation ended, the guardian told him that before the explosion, they would have only one last chance to talk to each other.
After finishing the communication with the guardian, Chu Yunsheng did not immediately let Buterne and the others come in for discussion. The impact of this matter on them wasn't big. They would still leave earth anyway. The one that was affected by this news the most was him. So he needed time to think about countermeasures alone.
Based on what the guardian did in the past, Chu Yunsheng had no reason to believe it completely. Before the space tunnel really appeared, he needed to use the rest of the seven days to prepare the backup plan in case something went wrong.