circuit time controller

[silviasol]

any way to control on time of a powered circuit.

[anvoice]

Does the on/off time need to be controlled via a microcontroller, or via potentiometers?

[anvoice]

Ok, then what sort of light are you switching? A simple small LED or a more powerful light that needs a lot of current? Depending on that you may or may not need additional circuitry.

You can go several routes. One way would involve using a very cheap Arduino pro nano and write a simple sketch that will blink your light. Advantage is that you simply input the seconds on/off, and it will adhere to it. Another is to use something like the 555 timer (probably the simplest thing you can use, but you will need to reduce the voltage to the 555 to below 18V) and adjust resistor/capacitor values to give you the desired on/off times. If you need to drive power-hungry loads, you may need to add something like a transistor to the scheme.

[Domagoj T]

Something like this?
https://www.ebay.com/itm/DC-12V-Infinite-Cycle-Delay-Timing-Timer-Relay-ON-OFF-Switch-Loop-Module-Time/112308185789?hash=item1a2616eabd:g:wsUAAOSwgY9XdQwe