I am getting ready to brew a Belgian Wit. How long do I ferment it in the primary before I transfer it into the secondary? How long does it need to stay in secondary?
People are getting out of using secondaries for all but the rarest of things, And opting instead for long primaries. So order something useful as your second vessel, get another primary bucket of a 6 gallon carboy or better bottle, with the headspace to actually be able to ferment another batch of beer in, so you can get your pipeline going.
You'll find that more and more recipes these days do not advocate moving to a secondary at all, but mention primary for a month, which is starting to reflect the shift in brewing culture that has occurred in the last 4 years, MOSTLY because of many of us on here, skipping secondary, opting for longer primaries, and writing about it. Recipes in BYO have begun stating that in their magazine. I remember the "scandal" it caused i the letters to the editor's section a month later, it was just like how it was here when we began discussing it, except a lot more civil than it was here. But after the Byo/Basic brewing experiment, they started reflecting it in their recipes.
If you are going to use a secondary (I'll answer the question instead of telling him to not use one), you can either check the gravity and transfer when the beer is done (you have reached the expected final gravity), or just let it sit for a 2 to 3 weeks and then transfer. Let ie sit in secondary for another 2 weeks or so.
Not everyone is abandoning secondaries. I tried skipping them recently and was not happy with the results at all.