A breach of contract occurs the party in breach fails to perform timely. Often, some leeway is given for time of performance.
It is not unusual for a party expecting performance to wait awhile (a few days, a week, maybe more) for the promised performance. Oftentimes, a phone call, email, or letter, can clear up when that performance will occur. If nothing is said in the contract about when the performance will occur, the law will imply a term of reasonableness under the circumstances existing at the time the contract was made.
Timing is important in many types of contracts. Such contracts often make contain an explicit “time is of the essence” clause, and spell out the consequences for failing to perform timely.