Barbara,
Just to overstate what Robin mentioned, if you are BUYING a property and using a funding source with no seasoning requirements (e.g. cash), there is usually not a proscribed holding period imposed on the buyer.
However, this is NOT ALWAYS the case when using borrowed funds. Many banks are starting to impose "anti-fliping" clauses / requirements designed to prevent investors from flipping short sales. These clauses typically state that if a property is purchased for less then FMV (meaning it was bought using something like a short sale), the purchaser (in this case the investor [you]) agrees not to transfer title to anyone else (agrees not to sell the property) within X period of time (usually 6-12 months). While I have not seen it personally, I chatted with an investor in California who told me some banks are even prohibiting "the transfer of beneficial interest in, use of, or profit from" short sale properties. This would mean an investor cannot purchase a property using some sneaky vehicle like an LLC and then try and sell the LLC's stock to short circuit the bank's anti-flipping / title transfer prohibitions.
Additionally, when the investor [you] is selling, it's critically important you verify, BEFORE accepting an offer, 1) who is purchasing your property and 2) what kind of financing they are using / what requirements their lender may impose on the borrower.
Some lenders have reached a point where they will not allow a borrower [in this case the investor's buyer] to purchase a property until that property has been held buy the seller for a specified peril of time (usually 3-9 months).
Hope this helps.
-Greg
Greg Wilson
The Real Estate Investment Mentor