You edit construction times in export_descr_buildings.txt in SS6.3\data. Each building has a construction time (in turns) near the bottom of it's entry. For example:
You change the timescale in descr_strat.txt in SS6.3\data\world\maps\campaign\imperial_campaign. Change it to 0.5 for 6 months per turn (i.e 2 turns per year).
If you have any other general modding questions, first check in the Mod Workshop (http://www.twcenter.net/forums/forumdisplay.php?f=272) before posting here. 99.5% of the time they will be answered there.