Hello,
we are 3 persons on a business trip to Zhengzhou and hebei county , we will be staying in Beijing from the 8th of oct till the 13th. On the 8 oct we are flying to Zhengzhou from Beijing and returning by train on the 9th, so we can feel the Chinese scenery on our way back.

My question is:
can we purchase a train ticket back without being sure of it's departure time? First class soft seat .will this ticket is good for all fast trains leaving for Beijing from Zhengzhou? Or do we have to know exact timing. Can we purchase these tickets one hour before leaving at the station or do we have to book in advance ? We are also not sure if we will board the train from Zhengzhou or from Xinxiang to Beijing