The ferry departs from the Xinshiqiao Pier which is about 7 kms from the Humble Administrators Garden. You could hire a taxi to reach the pier in 15 minutes. And, the night cruise will start from 19:00 every 30 minutes. Yes, the ferry will have a round-trip that will start and stop at the same place. It will pass by some scenic spots, such as Panmen, Xumen, Jinmen and so on, withou stop on the way/