When a contract includes a “Time is of the Essence” provision, delayed performance of the particular or general contract terms can lead to a material contract breach, says Alexander Barthet, an attorney at The Lien Zone.
Without this provision, a delay will not be considered a material breach so long as performance is effectuated within a reasonable time. However, with a "time is of the essence" provision, having an extension granted does not necessarily constitute a formal waiver. The Lien Zone advises all extensions granted be expressed in written form.
Read more at The Lien Zone.