On Or Before

"A phrase in a contract referring to the time for performance of a specified act, such as the payment of money or the closing of a transaction. Such a provision in a promissory note may be so written as to permit prepayment without penalty. If, for example, a seller wants a transaction to close in tax year 2017, the seller should not permit the purchase contract to have the closing set for “on or before January 1, 2018.”

Caution: some printed form contracts may pre-print the phrase ""on or before"" in front of the blank line to fill in the projected closing date."