You have completely missed the point. Seneca cared about using one's time wisely in order to maximise the meaningful accomplishments and noble conduct of one's

You have completely missed the point. Seneca cared about using one's time wisely in order to maximise the meaningful accomplishments and noble conduct of one's life. Whether time is illusory or real is irrelevant to his philosophy. One can only accomplish so much in life, and much of life is wasted because of poor choices of how to spend one's time. I've arguably wasted some of mine by writing this.