The correct answer is option 'D': The contract becomes voidable at the instance of the promise.

Explanation:
When it comes to contracts, time is often considered to be an essential element. The parties involved in a contract usually specify a particular time frame within which the contract must be performed. If the promisor fails to fulfill their obligations within the specified time, it can have implications on the validity and enforceability of the contract.

Voidable Contract:
A voidable contract is a contract that is initially considered valid, but due to certain circumstances or actions of one party, it can be voided or cancelled at the option of the other party. In this case, if the promisor fails to perform the contract within the specified time, the promisee has the option to either enforce the contract or treat it as voidable.

Key Points:
Here are some key points to understand why the correct answer is option 'D':

1. Time as an essential element: The question states that time is the essence of the contract. This means that the parties have explicitly agreed that performance within the specified time is crucial.

2. Failure to perform within specified time: If the promisor fails to fulfill their obligations within the specified time, they have breached the contract. This breach gives the promisee the right to consider the contract as voidable.

3. Voidable at the instance of the promisee: The promisee has the option to treat the contract as voidable due to the promisor's failure to perform on time. This means that the promisee can choose whether to enforce the contract or terminate it.

4. Difference between void and voidable: A void contract is considered to have no legal effect from the beginning, while a voidable contract is initially valid but can be cancelled or voided later.

In conclusion, if the promisor fails to perform the contract within the specified time, the contract becomes voidable at the instance of the promisee. The promisee can choose to either enforce the contract or treat it as voidable and seek remedies for the breach of contract.