Most recipes say to leave it in the primary for at least a week. You can leave it in longer if you're still seing lots of activity. At least 4 - 5 bubbles a minute. Just don't let the beer sit on the trub for more than 24 days or so. After you see all the signs of complete fermentation rack it into another carboy. You can let it sit for a couple of weeks. I'm doing a Belgian dubbel right now. It was in the primary for 12 or 13 days, now it's sitting in the secondary. I'm going out of town, so it's going to sit there until at least the 25th. Then to the bottles where it will sit for about a month before I sample it. Some people have told me that it should bottle condition for up to 4 months.