On the test ... Zombie is x 4 production and for a period of 12 hours. I don't understand the decrease to a x3 productivity and a decrease in the time from 12 hours to 3 hours.
I have friends over on the test server that are not actual guild mates of mine. I have yet had anybody dark buff me to date without previously checking with me prior to. I honestly do not believe any serious player would intentionally stop production on anybody's island ... instead it is just a way to get other players in your guilds to interact with each other. I know for a fact I would never darken an island without checking with the player to make sure they have the required light buffs prior to my buffing. The power of "whisper" ... players just need to use it prior to any dark buffing.