Time according to Seneca

Do in this way, my dear: make you the real master of yourself and appreciate with every possible care the time that until now has been carried away or runned away from you. Become sure that the reality is as I write to you: some hours are stolen from us by useless occupations, others get nearly out of our hands, but the most shameful loss for us is that which occurs due to our negligence. If you mind, a large part of life runs away from us damaging other people, the largest part doing nothing and the whole life doing different things from those we should do.
Can you indicate me someone who confers a right value to his time and day and who's aware that he's dying day by day? We deceive ourselves in this, by visualizing the death in front of us, like a future event, while the most part of it is already behind our shoulders.
Every hour of our past belongs to death's domain. So, my dear, do what you write me, take all the time you have to heart. You would be less slave of the future, if you became the master of the present. While we postpone our tasks, life flows away.
Everything, my dear, belongs to others; only time is ours. We got from nature only the possession of this extremely fleeting good, but we let whoever take it away from us.
And the human being is so unwise that, when he buy gold brick and in any case returnable goods, he accepts they'll be charged to him, but none, who was a waste of time for someone, considers himself a borrower, while time is the only good that mortals can't return, even if they want to.