Is Jiuzhaigou recommended in May

I am travelling to China in May 2016 with Chengdu as my port of entry/departure. I can visit JZG on either 4 -5 May or 30 -31 May. Which is a better time to go from point of getting better scenery and good weather. I am a serious photographer with preference for nature photography and hence the desire. I am aware Autumn is the best period but then we have to do this trip in May only. Is 2 days / 1 night good enough. Plus I believe it is a hugely crowded place - any tips to avoid the crowding.

Thanks in advance