Thanks Armaghan for asking us this question.
The term, is not until, is used to place some emphasis on the time of an action or event. So, the sentence “The deadline of the homework is not until next week” is intended to state that something does not happen before a certain point in time (i.e., next week) or before something else has happened. In this case, the deadline of the homework does not happen before next week.
The phrase “is not until” is considered positive because it means that there is still enough time or, in fact, plenty of time to complete the homework and carry it out. In other words, you don’t need to be so concerned about the deadline.