It depends on the laws of the state where the property is located. Most states have a process called a forcible entry and detainer. Talk to a good real estate/foreclosure attorney.
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There is a 10 day waiting period after the foreclosure sale date, at which time the bank will take title to the property, via a certificate of title. The bank, or the successful bidder at the foreclosure sale, can then send the Sheriff to the property to post a Writ of Possession, which typically gives the occupants between 24 and 48 hours to vacate the premises before the Sheriff comes back to remove everyone from the premises. You may be able to file a motion to cancel the foreclosure sale and attempt to re-open the case, but that is becoming tougher to accomplish. You should have a foreclosure defense attorney review your case and the filings to see if there are good grounds to stop the sale and litigate the case.
Many times you can contact the buyer of the property at the foreclosure sale and come to an agreement as to when to vacate the property. If you do not cooperate and vacate, then he must seek a writ of possession and have the sheriff's department forcefully remove you. The buyer can obtain a writ of possession anytime after the 10 day period subsequent to the foreclosure sale. At that point, it depends on how busy the sheriff's department is, therefore it is tough to give you an exact time frame.
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