Sellers here in the Ocala area will often accept an offer contingent on the successful closing of a buyer’s existing home. The buyers home must be under contract with a reasonable closing time of say 30-60 days.
Florida real estate contracts have firm performance dead lines. When negotiating a contract the buyer and seller agree on a closing date. In general we expect to close on the agreed on date.
A problem can result if the buyer is from a state without a firm closing date such as New York. In NY for example they close on or about a given date. I have no idea how people can plan their next move or schedule movers or anything that way. On 3 separate occasions I have had buyers from NY who were not able to close on time here in Florida due to some delay with their existing home sale.