is the time limit hard coded?

im playing a custom game with time limit as one of the victory conditions unchecked as i want to play a casual game to get to know the mechanics.

but now that i have less then 100 turns left out of the 300, its showing XX turns left to win! in the upper right hand corner.

since i turned off time as a victory condition, why is it even displaying that?

Because you left the Europe victory, it and the time win are pretty much different sides of the same coin. If you don't beat the king by then, then he wins a "europe victory". Or at least I believe that is the problem, hopefully some one that has chosen to play this game a few more times than I will confirm or reject this.

You can change the time limit via XML\GameInfo\Civ4GameSpeedInfo.XML
<iTurnsPerIncrement>900</iTurnsPerIncrement> is the number of turns in the game (900 is for example from marathon).

Turning off both Time and Europe victory should remove the time limit as well.

None of both will affect a game in progress.