This video features the Ven-O-Set, a 'miniature' mechanical timer which has a bayonet plug and socket. Intended to be installed in a ceiling or table lamp to switch it on and off automatically once per day.
This example from 1962 includes the original box and instructions.
As this must be fitted into a bayonet light fitting and can control only a single lamp, this was a very niche limited use product even when new.
Probably only used with a ceiling light fixture, as for desk or table lamps the far more common timers with a BS1363 plug and socket could be used, those also having applications for other appliances such as heaters.
Although miniature by 1962 standards, today this is a ridiculously large device to just turn a single light on and off.