Date of Train Reservation

Hi, I'm Ayu from Malaysia.

We traveling on early of May 2017. My question is I want to book in TCG website this week (March) but will travelling from Zhangjiajie Railways station (07/05/2017) to Beijing Railways station (08/05/2017). Is it the ticket begin sale this time or must 30 days before departure date? which station I collect the ticket in Zhangjiajie? Please advice.