I think you'd want to modulate it in order to adjust the holding torque.

But you're right - a 556 would provide the timeout and the reduction in torque. Although a 555 and a suitable transistor/resistor should pull VREF down to a suitable amount (much in the same way that Q2 does it).

Hell, you may even get away with a simple RC timer - assuming the clock's quiescent voltage is 0. That I'd need to think about (analogue electronics isn't my forté).