Wiktionary
phr. 1 Used to express a need for haste in action or response. 2 Said when something must be done immediately: When transporting organs for transplant, time is of the essence. 3 (context legal English) When used in a contract, places the other party on notice that failure to complete a required performance by a date certain set forth therein will constitute an incurable breach.
Wikipedia
"Time is of the essence" is a term in English and United States contract law that indicates that the parties to the agreement must perform by the time to which the parties have agreed if a delay will cause material harm. However, in the case of Foundation Development Corp. v. Loehmann's Inc. 788 P.2d 1189 (Ariz. 1990), in which the lease included a Time is of the essence clause, the court ruled a minor delay did not cause material harm and thus no breach of contract occurred.
Compare this to an "express clause", where a specific contract term must be performed to avoid breach, such as in the court decision in Dove v. Rose Acre Farms, Inc. 434 N.E.2d 931 (Ct. App. Ind. 1982).
Contrast this with reasonable time, where a delay in performing may be justified if it is reasonably required, based upon subjective circumstances such as unexpected weather.
Usage examples of "time is of the essence".
Any healer will have sessali herb in his stores, and for Mara, time is of the essence.
I suspect that time is of the essence, and if we can avoid a detour of twenty or thirty days to skirt the city, we should do so, but if we hear anything to indicate that Gracklstugh may be closed to our kind, we strike out into the barrens.
I suspect that time is of the essence, and if we can avoid a detour of twenty or thirty days to skirt the city, we should do so, but if we hear anything to indicate that Grackl.