what time the bus depart from Hubin to Earth tower ? will it drive us back to xiamen on the same day

Firstly, you must refer to Hubinnan Bus Station.

If you are referring to the earth towers at Longyan, the buses are scheduled at 08:30, 10:00, 11:30, 13:00, 15:00, 16:30, 18:00 and 18:00 for LY city. Upon your arrival at LY, you need to transfer to another bus to the scenic area.

Aside from that, there are buses directly taking you to Yongding Xiayang, where there are also some earth towers. They leave at 06:50 and 12:40. If you are done with visiting early, say, before 16:00, you can take a bus to return Xiamen.