After closing how much time does the buyer have before they vacate the property?
It depends. How much time was indicated on the contract? A question to consider. Is the Seller buying another home they need to move into and if so, where are they exactly in their transaction? Usually it takes about 30 days to close a 'smooth' transaction on a purchase. If the Sellers transaction turns out to be a nightmare than they can cause grief on your end. Not good.
Enter Occupancy Agreement. In most cases Buyers give Sellers a week to move out. If the Sellers need more time to move out you can have your Real Estate Agent execute an Occupancy Agreement so they pay you rent on a per diem bases (daily).
Work with each. Be understanding each others needs.
I'll assume you mean the seller as the buyer will be moving into the property.
I have seen it last as long as a year, it all depends on the situations of all parties involved. Some may want instant access and some may need to sell their home first(but didn't want to let a deal they could afford get away from them)and may offer a month by month lease/rental agreement. It really can be any amount of time agreed upon by both the seller and the buyer.
When entering into this type of agreement make sure you ahve all contingencies covered, I've seen people move into motels because the house they were moving into had a problem or the only way the buyer would pay a certain price would be contingent on access on a given date. It can definitely lead to major problems if not addressed and clearly defined UPFRONT.
In addition to the above answers, most conventional and FHA loans ** REQUIRE the buyer to take posession** within 30 days. One notable exception being an FHA 203-K which is a rehab loan and the buyer has up to 6 months to rehab the home before taking posession. This is done as protection for the lender to avert some investment property loans from being portrayed as owner occupied loans.
Check with the lender and see what kind of mortgage it is and what the occupancy requirements are. Having a "side agreement" with the seller doesn't override the lenders requirements. It's possible the lender could call the note "due" or flip it to an investment loan if you don't take posession. Probably won't...but it's possible.