Simultaneous mode simply mean that all players can make their turn at the same time. Whoever happens to login and make their move first will be first.
This game mode can be considered a bit more even compared to normal mode where some players get the benefit of being first on every turn.When the last player click end turn on a simultaneous game the game will enter a freeze period for a per turn random amount of time. This is to not make it aadvantage to move last and then move first on the next turn. The freeze time will be a couple of hours and all players of the game can see how much time until thenew turn starts. Games that are in freeze mode have a snowflake on them.