vDip's stats page says that games last for around 33 turns (where turns is spring or fall). Assuming that there are only two of {spring retreats, fall retreats, builds} per year, then you're looking at 6 hours of gameplay. If you get both retreats and builds each year, and no-one hits ready, then you're looking at an 8 hour game.
We're planning to add timed phase changes as an option for live games (say first 4 hours live, then it becomes 1 day phases, or something), but in the meantime we have to do that manually. If you want to do that, shoot
[email protected] an email and we see if we can arrange someone to be on at the right time to manually change the phase length.