How long does it take to Finish one game?

with 297 planets that is probably normal, if you play online most games will never go past 2 hours, or if it is a 5v5 there will be rushing and the game could last less than an hour. it all depends how you play and who you are with.

against ai if you do a large random single with teams it would probably take 2-3 hours depending on how well you can beat the ai.

Games with hundreds of planets are not normal, and can last a very long time.  I've never played a game with that many planets, so I can't tell you how long it should take, but my longest game was a 100 planet game with 5 stars and 5 AI's (all enemies) which lasted seven hours.

A lot can affect the length of a game.  The layout of the map, the way your enemies behave, and just a random stroke of luck can greatly change the time the game takes to play out.  In a 1v1 game on a small single-star system, matches can last 30-60 minutes.  On larger maps it can go accordingly longer.  On big maps, 6 hours isn't uncommon, but longer than that is an oddity.  However, as I said games with hundreds of planets are not normal to begin with.

A small map usually has 5 colonizable planets per player, a medium one has 10, and large ones have 20.  Your map has 60 planets per player, easily putting it in the gargantuan (ie, off the charts) category.  Maps that big become a giant game of cat and mouse, because there's just so many planets and only so many units to form your fleet.  That can take a long time to resolve.

To be honest it depends on your game style of play. Like Darvin3 said above your map is beyond huge. So expect it to take even longer.

Also this game is not a fast paced RTS. Like it was said by both Darvin3 and top vasari, MP PvP doesnt take to long mostly game 1-2 hours. With longer games 3-6.

But against the AI you can expect game to last 6+ easy all depending on map, what AI you pick, the speed options, and your game play style. I play very very long games vs. AI. My typical game on a map is around 16 hours of game time. Longest one lasted about 36 hours total. I do play on super slow alot of the time just for fun. So that why my games are so long.

So whats normal to me is fast to most. It hard to tell you whats normal, there are to many factors.

Man, I must suck. Took me 4 hours for a small random map, on Easy.

I find it pretty hard getting things to move fast. Espesially getting minerals etc.

There are settings in the options that allow you to speed things up like mineral production and credit income.

The game was designed to play at your own pace. Some can play a quick (few hour long game), or a long epic game. In systems of war with 4 hard AI's it takes me up to 6 hours to defeat them all. It isnt about speed its about strategy.

1v1 with a computer is about 10-30 minutes (with quick start) and depending on the size of map and difficulty (longer for higher difficulties).  newer people will probably have harder time, but it's quite easy to beat the computer after you've played and learned the ropes a bit (or have past experience with these types of games).

3-5 player FFA on small to medium maps might take 2 to 3 hours depending on skill and difficulties. 

Anything higher than that will be 6 hour affairs and I hope the next addon will add some end game options to ease the victory conditions (universal culture victories or some such). 

Also, any game where you have multiple stars or more than 50 planets will be an automatic 6 hour affair unless you lose out early or are playing with other humans in teams.

Note that most online multiplayer Sins games don't take more than 2 hours to resolve.  Why?  because in a 4-v-4 you personally don't have to take down all of the enemies--you have allies to help mop up the map if your team wins.  Also, once the game has been decided and it's no longer competitive, people will often say "good game (gg)" and quit or surrender, allowing the games to end without having to go through the boring motions of mopping up defeated enemies.

I would say at least 8 to 10 hours