A standard motor with an encoder wheel would do the trick.
When the clock hand reaches the desired position and the motor power is stopped wouldn't the weight of the clock hand then contiue to move the hand by gravity until it pointed down to 6 o'clock? There is no 'holding torque' on a standard DC motor when there is no voltage applied to it and any continous voltage applied to the motor would cause it to turn continously at some speed.
I think a stepper motor with an additional index sensor or absolute encoder would be the best solution.
Lefty