Can I exit & re-enter China by Z97 train(Beijing-Hongkong) and Z98(Hongkong-Beijing) in 3 days?

I have multiple entry visa, each entry 60 days. Before my 60 days are up, I plan to take the Z97 train(Beijing-Hongkong) on the first day, leaving Beijing West Station at 12:40, arriving second day at 13:01. Can I take the Z98 train (Hongkong-Beijing) on the second day, leaving Hongkong at 15:15, arriving Beijing at 15:30 on the third day? Will I have enough time between 13:01 of arrival and 15:15 of departure? Will this fulfill the requirement to exit China and re-enter China? Do I have to exit the train station when I arrive in HongKong and re-enter to depart HongKong? How do I book the return train tickets?