How long it takes will depend on the speed of the underwriter and the orderliness of the application packet you submitted. Thus, the underwriting stage is one of the biggest variables. It could take anywhere from 5 – 25 business days, or even longer. It will also depend on how many people are involved in the process.his is when the terms of the loan are established, and when the lender and borrower commit to the agreement. It might take anywhere from 1 – 5 business days to complete this stage of the process. 2. Processing and underwriting: You’ve agreed to the terms of the FHA loan, and you’ve signed a document to that effect.