I don't think there is a meaningful average turnaround time for longarmers. Some won't even accept a quilt if they have more than a given number in their queue. Others will take them in, but they may not get finished for several months. Some are busy, some are not; some (with robotics) can finish a couple of quilts a day, others may do custom quilting that takes a week or more. And then there's my longarmer friend who just broke her wrist and cracked 3 ribs. She won't be able to quilt for a while, but I'm sure she has notified her clients if their quilts are waiting to be done.