How long does it take to get to Beijing South Railway station from Beijing West station

i don't think 55 minutes is enough. It takes at least 20 minutes by taxi from Beijing West to Beijing south, but it can be longer if the traffic is bad. you also need at least 1- 20 minutes to leave the Beijing West station and wait for a taxi, and another 10 -20 minutes to enter the Beijing South station, check in and get to the platform. so i suggest that you change a later one from Beijing to shanghai.