Rule of thumb is hair grows the fastest when we want it to grow the slowest.
I started letting Joey's hair, on the bridge of his nose, grow out to reach his topknot last May, it will go in a band if I put the band really really low; it's taking forever to grow, but when I was trimming it, once a month was needed. Pin brushes are best for dogs with long hair, and one of our members sells a very nice Madan Pin brush. You want something that doesn't scratch the dogs skin, yet has no balls at the tips that break hair.