USDA doesn't have any specific restrictions on property flipping - they charge the lender with the following: 
Property flipping. It remains the lenders responsibility to ensure any recently sold property’s value is strongly supported when a significant increase between sales occur. The lender must perform a thorough review of the appraisal report to validate and support the property’s value and protect the applicants from possible predatory real estate lending.

Original question:
What are the flip rules for USDA?