How soon can a mortgage company evict you after a sheriff sale?

Until the new buyer files an unlawful detainer action with the court and receives a writ of possession from the Court

The mortgage company has to file a lawsuit in court called unlawful detainer. It is the same type of suit that a landlord files to evict a tenant who hasn't paid rent. When your lender files the suit, you will be served with a copy of the complaint along with a summons. Read the summons carefully for instructions on responding to the suit. You have only five days to respond. If you do not respond, the lender will win by default and get a judgment against you. If you do respond, the court will set the case for trial. Unlawful detainer cases get calendaring priority, so the trial will be set soon. If you lose either by default or at trial, the court will issue a writ of execution, which gives the sheriff the authority to move you out of the house. The length of time takes varies from county to county depending on how busy the courts and sheriff's department are and how diligent the lender is in prosecuting the case. You should call the sheriff in your county and ask how long they are currently taking to process evictions. But, if you haven't done so already, you should start looking for another place to live right away.

It is generally only 10 days but often and surprisingly, the mortgage company will allow you to stay past that upon written agreement, and especially if you agree to clean the property and leave it in good condition. There is something called a "cash for keys" program as well. Contact the mortgage company ASAP to discuss what they will agree to and possibly an attorney to assist with massaging and expediting the communications