That depends on a lot of things:
The type of knife you want
Whether you want an existing design or a new design
How long you need to approve the final design
The complexity of the fabrication
What materials you want (and how long it will take us to get them in stock)
For most new designs, the design process generally takes one or two weeks; fabrication can take anywhere from 3-4 days to 3-4 weeks, depending on the design.  Nathan’s currently scheduling new projects at least 6-8 weeks out, and that lengthens in the months leading to major holidays.
Contact us, and we’ll be able to give you a closer estimate.