Simple, and the easiest way would be, to program arduino so that once turned on it will feed the LED and make the countdown (in milliseconds = 7200000) Scheme: ARDUINO (basic programming for RELAY control) + RELAY + LED If the arduino power is cut off, the LED will be off since the RELAY will not let energy pass. Once you turn on Arduino, the RELE turns on and passes power to the LED and starts the countdown Once over 7200000ms, the RELAY will turn off and will not come on again until you turn off and then turn on Arduino again. Only I see it absurd to spend an arduino for this, but seeing that you do not have much idea it is better that you start trying this and if you already catch up, you can put an LCD screen, a couple of buttons and a relog to control the start and end time. Arduino by itself does nothing, they are all orders programmed in C is simple, very basic and you have examples in the Arduino itself or you can search online or ask in this thread and I help you with the programming. Even if I spent an arduino for this, I would buy a simple programmer that does all this by putting your time, an analog programmer costs just € 5 and digital just over € 10