You can play Cyber nations for as little as under 1 minute per every 24 days if you would like. You won't get much out of it, but thats the bare minimum to be active. If you want to get involved I would suggest joining an alliance which can help teach you the best way to build your nation, teach you about the world here, and keep you engaged and as active as you want to be.
There are different alliances geared towards different outlooks and different styles. Some alliances are more apt to war, others are more apt for peace. Others rarely fight wars, others fight in just about every big war. I'd suggest looking around and talk to different alliances to see where you would fit in best.