Turns are set to advance once every 24 hours, or when everybody has their orders in. If you can check in about two or three times a day for a few minutes at a time, that'd be fine. Technically once per day would do, but it's considerate to think about not slowing the pace for others.
For the game itself, planning and dealmaking is the most timeconsuming part. The orders themselves don't take more than a minute to get in.
Your mileage may vary.