This is a Smiths 5 hour mechanical (hand wound) timer, produced from 1969 to 1971 - model number QLR 900. I was lucky to get the timer in it's original box!
Smiths Ringer TimerInstructions:
To set the timer turn dial clockwise past setting line then back to time required
This action automatically winds the mechanism and starts the movement.
For a period of less than five minutes turn the dial past 5 then back to the required setting.
This box is not suitable for transmission through the post without additional protective packaging.
Made in Great Britain