Your castle never sleeps, but you can! As a new player with a single village, you do not need to worry too much about the safety of your castle. While the AI in your parish may ransack or pillage your village, they will not destroy it completely. Higher ranked players are also unlikely to attack you, since they will incur a high honor penalty for doing so and get very few resources in return. If you have a liege lord, the attacker will have to answer to him as well! Being friendly with the other players around you is an advantage here as well, since you can work together to deal with threats. As you progress in the game, you can also research monks and use their interdict skill to make your village unattackable for periods of time.