IIRC the turnaround time averages 4 weeks. Had to send mine back last year sometime when I junked it and got it back in 2 weeks but they said to expect more. I think that it varies based on where they are in production / how many orders they have coming in. If you call them and ask someone they'll give you a (more) definitive period. They're usually pretty good to work with.
What's your rack getting rebuilt for?