Dear Mr. Faith Adam, the visit to Great Wall will be a bit rush but is available for your schedule if you are ok with it. The transfer from Tianjin Xingang Port to Beiijng Mutianyu/Badaling Great Wall takes about 3.5-4.5 hours, that depends on traffic situation on that day. And Great Wall usually close to public around 5pm which means the rest of the time will be blank. Of course our guide and driver could show you around in the city or to the Olympic Greens which is nice in the evening.
Transfer from Tianjin International Port to Beijing with independent car/van and guide is US$84 P.P for two persons' group. While one day Mutianyu Great Wall tour is US$145 P.P for two persons' group.
Another way to make this trip is take a taxi to Tianjin train station and buy ticket for Beijing, which is half an hour's driving and our guide & driver could meet you at train station to start the tour.
Please feel free to contact my e-mail address if you need any further assistance/information. Nice day!