Just a little over a month since I bought the yarn, and I finished it off this morning. I think that may be some kind of record.
As soon as I finished weaving in the last end, I put it on him. Since his natural tendency when I get down on his level is to run over and give me kisses, getting a good shot of it in use proved a bit more challenging. It's quite form-fitting, which is exactly what I was going for, and he's very pleased with it.