Hi, kindly advise how to tour the tulou in Nanjing after arriving at Xiamen bullet train station.

Will you arrive at XM North Railway Station? If yes, the distance is about 93 miles (150 kilometers).
You can take high-speed train to Nanjing Railway Station first. After arriving, you are advised to hire a private car to the scenic area. The fare is CNY 400-500 for the round-trip.
Generally speaking, the suggested sightseeing time of Nanjing Tulou and Yongding Tulou is two days. But if you hire a van and tour around quickly, you can finish the tirp in one day. :)