Depends on number of factions you are playing with and your computer specs, also if you're playing with 1.61 or 1.7.

Here are options to potentially speed up the turn time.

• According to others disable lean maps (however, haven't tried this myself)
• Don't use exploration treaties. (in large maps with 50+ AI)
• Must have 16 GB Memory or more.
• Build ques for 1.7 beta drastically increase turn time and game lag, one could try to turn off auto upgrades to shipyards, then reducing each star base build que to less than 2.

Hopefully that helps.

I zoom in on an unexplored area of space when turn times start to take a while, that get's all ships moving instantly and cut's it down significantly!