A simple long duration or long delay timer circuit can be built using a single 555 timer IC and few external components as shown in the figure below. The project can be used for variety of timing applications. The circuit can activate an LED and a relay switch for a preset time period and can control
any AC or DC device connected with the relay.
The 5M variable resistor is used to select the desired on time duration of the LED and relay. The capacitor Cx can also increase and decrease the time duration. With 1000uF capacitor the circuit can provide max time duration of around 12 hours. By increasing the Cx value to 2200uF or 4700uF can increase the time duration upto 24 hours. For making the circuit more simple you can also remove the LED and 470 ohms resistor.