I don't agree with that. Seasonal turns, while keeping the overall time frame of the game from 1087 to 1453 would blow this game out of proportion. All build times would need to be rearranged or you would need to wait ages for your castles to upgrade, and if downgraded you would see fortresses all over the place around 1200ish. Besides, the number of provinces won't change so chances are you'll have finished your campaign before even approaching High Era.

I haven't been to the Colosseum that often, but I think there will not be turns in Rome, the time will pass continually, so you probably have a slider to increase or decrease the passage of time.