There is no clockwork mechanism in the ST901. Clockwork mechanisms are for timing a fully open shutter. The higher speeds are achieved by narrowing the distance between the shutter curtains as they traverse.
The ST901 has essentially the same mechanical shutter mechanism as the ST701 and ST801 manual exposure cameras, but does not have their clockwork mechanism to time speeds slower than 1/60, so it has no manually selectable speeds slower than that except B, nor does it have any speeds which are manually selectable and electronically timed. The manual speeds it has are mechanical and fully independent of battery power.