We plan to fly from Chengdu to Jiuzhaigou on 13 Apr. Is it advisable to fly at night?

I took a plane at night between the two places. It is ok. Don't worry!

I am wondering whether you mean the road condition from the airport to Jiuzhai Valley area or Chengdu city? If it is to the valley, there are several sections of hilly road. You'd better go there in the next morning in case. If you mean the city, it doesn't matter at all. The road condetion is very good.

As for the van, I suggest you rent one in advance for convenience.