Thank you for your advice, Sir, but I couldn't understand, so is it a problem or not ?

It will turn on a light for the shortest duration of 30 minutes.

 

Use a solid-state relay controlled by the Arduino to switch AC power.

 

If your Arduino has a crystal, you don’t need a real-time clock chip.

 

If your Arduino has a crystal, you don’t need a real-time clock chip.

So you are saying that I can built a timer by using the oscillator that are already on it chip ?