heyy :D
how do I set the plugin if I want a free raid protection is activated for 18 hours when the player goes offline?

If you want to offer free protection, setup the cost settings like this:

  "Cost settings": {
    "Material cost multipliers": {
      "twig": 1.0,
      "wood": 1.0,
      "stone": 1.0,
      "metal": 1.0,
      "armored": 1.0
    },
    "Default hourly building cost": 0.0,
    "Default hourly base cost": 0.0,
    "Default structure damage cost": 0.0
  },

As for free protection activate for 18 hours, it is currently not possible to give certain protection for X hours. By the nature of the plugin, protection lasts for as long as the player can afford it.  You may be able to achieve this by getting a little creative and combining this plugin with others if you setup a protection level that is free, grant players that protection level when they logout, and then revoke that protection level after they have been offline for >= 18 hours.

Other than that, I suppose this would be a suggestion for this feature.