The purchase agreement should address when possession is to be delivered. If it is silent, possession is to be delivered at closing. Neither party can unilaterally change the deadline for delivering possession.
If the seller refuses to close unless the buyer agrees to delayed possession, the buyer should schedule the closing, notify the seller of the closing date, time, and place, and then show up. If the seller does not close, that would set up a claim for breach of contract to obtain specific performance and/or damages. Such a suit could take more than 6 months to reach the end but that is rarely necessary. The parties usually reach a resolution once they have to engage attorneys. In your case, the seller may not be willing to risk the loss of the sale and may be counting on the sales proceeds to pay for the new place.
If the seller closes but then refuses to leave, the buyer can bring an eviction action. The notice requirement is usually 7 days; if the seller is not out by then, the buyer would proceed with the summary proceedings. A hearing usually follows a week or two thereafter and, if the seller has no right to stay, the court will order the seller to leave within 10 days. This may get the seller a month or so.
Answered on Nov 27th, 2018 at 2:20 PM