anywhere from 2 hours to 200 hours. when i bought my long-arm the lady at the shop i ordered it through told me anyone can quilt a queen size quilt in 2 hours with this machine...10 years later i still have not managed that but i can do a baby quilt in 2 hours :)
it takes 45 minutes of more just to load the quilt; unloading does go a bit faster, but even baby quilts from the time i walk into the room to load till i unload and walk out is a minimum or 4 hours.
if the quilter works out side her quilting business (like me) i may load a quilt on sunday and get the first row across done, then stop. after work monday maybe go work another hour...ect so it may well take a week or two. it depends on lots of stuff...including dealing with tension issues, thread breaking problems, lots of stuff, so i don't think anyone can really say, i can quilt a quilt in 2 hours...maybe but not usually.