This is a complicated question and varies depending on the time of year, size, and scope of the piece. In general, I run a 2-3 month backlog.
Custom/Heirloom quilting takes time. The creative process of designing a quilting plan takes almost as long as the actual quilting. You spend hours and months making your quilt top, I will not rush. Plan accordingly. I promise you, it is worth the wait. Anyone who claims they can quilt your top in a week or less is doing you a disservice.