It takes a satellite 1.76 h to revolve around an unknown ast

It takes a satellite 1.76 h to revolve around an unknown asteroid in a circular orbit of radius 540 km.
How long it will take an object without initial speed to reach surface of the asteroid from this orbit?The radius of the asteroid is very much smaller than radius of the orbit and can be considered negligible.
Answer in units of h
The answer is not 0.3963 h.Tell me why!
Many thanks!