The flight of Changsha airport was delayed due to the weather, and it was ready to alternate to other airports in the early stage. In this case, do we have to wait until the pre-flight arrives?

In general, you need to wait. If it is a big airline, it may transfer your plane to pay for the flight. If it is a small airline like Chunqiu, it is impossible. But you are on standby because of the weather. Even if you are transferred to a plane, you can't get in or fly. So in a word, you have to wait.