I've played other online games that, when moving to new stages, would have announced the users at least 1 week before stating the exact day and GMT hour the new game will start on. You have to assume that not all your players are online on your game every day, and that they could miss a few days, being offline for different reasons. A longer waiting period between announcing the new version and actually starting it wouldn't have hurt - quite opposite, it would have generated more hype (not that the game needed it, anyway).
So, thank you for your answer Sami, looking forward for the new game.
Btw, joining the other active games is not an option, I wouldn't stand a chance at 42% and 60% game progress. I've did that once, with Modern Times #1.