It can be played with only two. The way it works is that the you play a different map depending on how many players are present (So that you're always forced onto each other's space). I've only played it once and we were actually 1 player above max, which still worked pretty well. I could actually see one more player fitting on the board, but the way the way the races work that might get annoying.
Our game lasted about an hour I think, but only two of us had played before so we were taking our turns slowly. I didn't time it, but it felt like about an hour, which is pretty good considering the amount of people playing. When your turn ends you reap the benefits of all your actions, so that someone can wipe you off the board immediately afterward and you will still play on with a new race.
When I say it maxes/ends at 8 turns those turns are actually more akin to "rounds". You go around the board 8 times with each player taking a turn, so 4 players would actually take 32 turns since each of them will have taken 8 by the end of the game.