\Assets\Scripts\Campaigns\*.mct :
Era=0,1 or 2
\MetaAssets\ServerProfiles\SinglePlayer\Time.gf :
You can modify TurnsPerYear, MilliSecondsPerTurn, DelayBeforeFirstTurn under [Clock] but it is best not to modify the settings under [Clock/StartingDate] rather set the Era in the desired campaign files.
If your mod modifies these files, it should back them up for restoration on uninstall.