Hot water boiler & timer no stat

Anyone, ever install a timer for hot water boiler, did an inspection 4-months ago, client has called for information on how to set timer for boiler ,I told her to call a heating guy, I am still wondering how it is set up.
I get this type on older Chicago buildings with old hot water systems. just never new how they get set up?

Timers have many uses they are just a switch and can be normally open or normally closed or a combination of both.

Normally used to turn on or off any number of types of equipment. Boilers, A/C units, Hot water heaters and the list goes on and on. Most commonly used to activate the defrost cycle on refrigerators and commercial refrigeration coils.
The timer face is normally a wheel with the days of the week and 24 hour setting for each day. This wheel has pins that screws into its face that trips a switch linkage thus activating or deactivating a circuit.