I brewed a NB #8 (which is a dubbel) and left it in the primary for more than 5 weeks and then moved it to the secondary for more than 3 weeks. NB instructions call for 5-6 weeks of fermentation and then up to two in the bottle. Everything I read though says leave it go as long as you can. It's been in the bottle for a week and hard to resist, but I am going to do so as long as I can. I want to give it atleast three weeks in the bottle before I crack open the first one. That will be about 3 months since brew date, one month longer than NB instructions call for. I plan to let it last as long as possible.