With a USDA loan you need to basically fully underwrite the entire file. From there the file is sent to USDA for their approval and then back to the lender to close. The time it takes the USDA to look at files can be found by calling their office. I don't have the number at this time but in the past the range has been anywhere form a few days to over 15 business days. This would be important to know when submitting and offer on a home with this type of financing so have your lender check on these turn times for you as this will also effect your lock.
Best of luck to you.
REALTORÂ® | Mortgage Broker
Keller Williams Realty | 360 Lending Group