How long to design a game?

I don't think that there's a "best way" of doing it. Whatever works best for you!

Personally, I enjoy entering games into competitions. Not only can you get feedback on your game that way, but having to meet a deadline is a greta motivator to get a game "done", especially where ruleswriting and playtesting is concerned.

I do think it is important not to rush a game during the early stages of the design, when you still have to the think out the basics. The basics should be there already, well thought out and working, and then you (read: I) need a little kick in the butt to actually make the game.

I came up with the idea for Gheos early in 2003, inspired by the now infamous "Doomed Civilization" competition on this board. I think I spent about two months tweaking and playtesting the design before submitting it. Afterwards I kept on tweaking and streamlining and playtesting the design, until I finally found that I couldn't make it much better. The basic foundations of the game never changed since spring 2003, but the details certainly did and are what, I think, make the difference between a nice game and a great game. The game has been picked up by a publisher and will (hopefully) be published later this year.

So, while the actual designing of the game took no more than 2 months, honing it into a design that was actually good enough to get published took almost 2 and a half years.

Again I want to stress that whenever you move ahead with a design, make sure the basic foundations are really solid, otherwise it will be hard to streamline and tweak the game into perfection later on.