I only have three days in this region. After Hualong I want to see Jiuzhaigou, either fully two days

In my opinion, you had better stay two days in Jiuzhai Valley.
I do not think Songpan Ancient Town is worth seeing, because many of the architectures locally are newly built. I do not prefer it. In contrary, I like the Jiuzhaigou very much and it is worth spending some time in the park and I am sure you will not feel regret.