Is 1 day enough for visiting Jiuzhaigou valley, or it's going to take 2 days?

Generally speaking, a single day is ok for your to see most scenic areas in the valley. If I were you, I would stay in the valley for two days during its low season (Nov.16 to Mar. 31). A one day ticket costs 80 RMB and you just need to pay another 20 RMB for a second visit on next day. However, you need buy the sight-seeing bus tickets again during your second visit. During the peak season, the second visit will not be available. If you want to stay for two days, you will be asked to buy the entrance tickets two times.