I wrote a piece a few weeks ago about balancing games for movement. This time I want to focus on completion time. Let me tell you; there is nothing more humiliating than a bunch of people who have set aside time to play test your board game that you said would only take an hour, then witnessing as they casually check their watch now that your game is taking way longer than it should! This happened to me numerous times. When a game designer (me) feels the need to shut down playing his own game because he/she can sense people are getting bored and checking out, you know you have a GIANT red flag. I mentioned this before, but it's absolutely critical that you nail down your game time.
Bottom line is, unless you have the next Monopoly, and let's be honest, who really wants to play Monopoly, your game really shouldn't take more than 120 minutes to complete. This should include setup and rule reading. I don't make the rules, so you can do whatever you want. Just make sure that your game is engaging enough to merit a longer play time. And don't be too proud to make cuts where you need to. As I always say, it's better to put the work in and even scrap the whole project if it means you'll get a better end result.