time delay switches or timer switches

It's a switch* which operates after a delay (adjustable) or at a specific time (adjustable).

Do you have a central heating system?.... If 'yes' then go and look at the timer.
Also consider a simple alarm clock.

* The switch is usually an electronic device closing the circuit or mechanical contacts closing an electrical circuit.

Del

or opening (on-delay and off-delay)

www.time-mark.com has some good diagrams which will give you a circuit view.

James