[@Kangutso] ah, the dreaded question... I don't know how much time passes, realistically. Your population grows with every turn so perhaps your posts are a summarize of your yearly activities, or perhaps your post focuses on a few key events during the amount of time that passes.
Let's say... A year? It's up to you, really. Mechanically-wise, one turn could be anything from half a year to a couple years, but nothing more or less than that probably. Although this would seem odd sometimes due to mechanics such as prospectors take an entire turn to return with their findings of exploration etc, but hey, sometimes mechanics and realism don't entirely flow together well.

TL;DR: I don't have a good answer. Think about a year per turn.