Buy a bullet vibrator.
Cut the cord, put the vibe into the head, use the power wires to control the motor on/off time.
Next, use one of the smaller Arduino boards.
The event happens, a small relay is energized, the motor rotates and vibes, the time runs out the relay is deenergized, the motor stops.
Better yet, drive the motor with a MOSFET and use PWM to get differing rates of vibe.