Consider whether this clause benefits your party. For a supplier, the Time is of the Essence clause can be reviewed to consider whether a party is in breach for slow delivery of a product ,if the product is not delivered on time. It can also be invoked for the purpose of requiring prompt delivery of a product return. But in either case it would be useful to specify who or what is intended to be protected by this clause, so that it does not inadvertently negatively affect your client.