What does Seneca's Letter 1 say about saving time?

Seneca opens his Letters to Lucilius with a short, pointed letter titled "On Saving Time." His argument: "Nothing, Lucilius, is ours, except time." Everything else we possess — money, property, reputation — either belongs to someone else or can be taken by someone else. Time is the one possession that is genuinely, exclusively ours, and yet it is the one thing people squander without a second thought. Seneca observes that people guard their money and property carefully, resenting anyone who takes even a small amount, but let other people and distractions steal their days without complaint, as if time were the cheapest thing they own rather than the only thing they truly have. His advice to Lucilius is to audit his own life: "set yourself free for your own sake," gather and save the time that has previously been wasted, wandering, or spent on other people's business. He famously observes that we don't feel poor when we lose time the way we would if we lost money, because time's loss is invisible — it "slips away" — until old age arrives and reveals how little was actually used well. The letter closes with the instruction to hold every hour in one's grasp, since depending less on tomorrow means depending more on the one thing actually in hand: today. For Seneca, this isn't a productivity tip — it's a claim about mortality: since none of us knows how much time remains, treating it as expendable is the deepest form of self-neglect.