https://m.earthempires.com/...change-31871?t=1409691527
Tldr:
Play turns at midnight. (no bonus)
Country play 18 hours later (gets 6 turns from 12h & 18h bonus)
Country plays 4 hours after that (gets no turns)
Country plays 8 hours after that (gets 3 turns from 12h bonus)
Country plays 6 hours after that (gets 3 turns from 18h bonus)
Country plays 8 hours after that (gets no turns)
Country plays 10 hours after that (gets 6 turns from 12h & 18h bonus)
Country plays 72 hours after that (gets 6 turns from 12h & 18h bonus)
Country plays every 2 hours for 24 hours, gets 3 turns at 12h and 3 turns at 18h.
Thus, if you play every day, you should get 6 turns bonus per day, on average; you don't have to wait for the 18h mark, you can play at 16h and then 2h later at 18h to get your bonuses.
Technically, if you play every 6 hours all set, you end up with an average of 8 turns per day, over a 72h cycle. However you'll have a smaller PM &etc; if there ends up being any sorts of abuse with this we can always tweak stuff, but I don't anticipate anything too extreme.