Buy at station - not presale

Hello. We are thinking of going from Shanghai to Suzhou but we do not want to buy pre-sale tickets because if we are too tired, we might not go. So to have flexibility, can we just buy at the Shanghai bullet train station if we decide to go? Our trip will be around April 20, 2017. Also, how many minutes or hours do people usually have to wait at the non-Chinese window? Thank you.