The 45-day identification period is the window, starting at the sale of the relinquished property, in which an exchanger must identify potential replacement properties in writing.
The 45 days begin on the day the relinquished property closes, and the identification must be in writing, signed, and delivered to the qualified intermediary or another party to the exchange. Each property must be described unambiguously, such as by street address. Because the clock does not stop for weekends or holidays, experienced exchangers start shopping before they list the property they are selling. Naming a backup candidate or two is common, since any property that is not identified in time cannot be used.