When you go idle you can be attacked for up to 6 hours afterwards. This means you can leave your character in game to allow others to attack you. This will also activate if you have not used the game in a while to preserve game resources.
This is the message that displays when you go idle:
You have been disconnected from the game because of inactivity. This prevents players to overload server when they are not actually playing. While you are offline or idle , all your stats, creature age, and other timers run as normal. You don't have to be online to regenerate vitality. While you are in idle mode you can be attacked by other players and you appear as online (but idle) to the other players. If you wish to exit so that you can no longer be attacked please logout. Closing this window keeps you in idle mode.