Do you mean how long does an appraisal on your new home take using a USDA loan?
If your lender is experienced and knows the process, usually less than 3 weeks. Some lenders are not experienced/connected and can take significantly longer.
Be sure to check out the USDA website to determine if a property qualifies before planning to use this type loan. Also, if the home has a pool, that value will be excluded from the appraisal and you will need to pay cash for any short fall between the appraisal and the purchase price.
Don't forget the income limitations that also apply to a borrower.
Call me an I can get you the name of two lenders to consider.