Tux is right, it only takes 5 minutes per turn. Maximum 30 minutes for no-RP. But if you're the kind of guy who can't put down something for two or three days and come back to it, SE:IV isn't for you. For me at least, I tend to think about it in between, making strategies, but that could be distracting.The data files are a nightmare to read through and I just don't have the time.
Here are docs for Adamant Mod, should be more user friendly.
<edit>If you've played SE:IV stock before, going straight to another mod isn't any problem at all, especially well-made mods like ST Mod or Adamant. But if you want perfection... and you'll be playing everybody with experience under their belt... there's certain tricks you don't get unless you've played multiplayer before but that's the same with everything... if you look at the first few pages of the original Space Empires thread with the most views, especially when it talks about overall strategy, that should give you a good primer, and the MIN/MAX guide posted earlier...</edit>
Brian