You have tried the trick where you tell them the reservation is thirty minutes earlier than it is. It works, for a while. Then it quietly stops working, and something else breaks along with it.
The Trick Stops Working Before You Notice
Give someone a false start time and they show up thinking they beat the clock, when they were right on schedule the whole time. It solves the evening. It does not solve anything long term, because eventually they catch the gap, or they start second-guessing whatever time you tell them, whatever the reason. What you are managing at that point is no longer their arrival time, it is whether your word can be trusted, and a relationship does not shrug that off even when the motive was patience rather than manipulation.
Sermons Do Not Change a Clock Habit
Telling someone that they are inconsiderate for showing up late again produces one of two results, and neither is punctuality. Either they get defensive and list the one time they were on time, or they feel bad for an evening and repeat the exact same pattern next month. A long-established relationship with time does not bend to being told it is wrong, because the lecture is aimed at conviction and the habit was never about believing punctuality matters. What moves the needle is a cost that shows up on its own, right away, without a speech attached to it. Eat when you said you would eat instead of waiting past hunger. Start the meeting on time and let the late arrival catch up on missed ground alone, with no recap held open for them. That is a consequence, not a punishment, and the difference is that nobody delivered it as one.
Describe the Behavior Instead of Naming the Person
"You are always late" hands the other person something to fight, because now the conversation is about whether that is even true, and they can win it by finding one counterexample. A sentence built around what happens and what it costs you does not offer that exit. Something closer to "when the start time slides by twenty minutes, I end up feeling like the plan came second" describes an effect instead of a character flaw, and it is much harder to argue with a description of your own experience than with a verdict on someone's identity. One version invites defense. The other invites an actual answer.
Decide What You Are Choosing
At some point the real question stops being how to fix someone's clock and becomes whether you are willing to live with it or willing to change what you expose yourself to. Living with it means the lateness still costs you something, but you have stopped treating it as a daily fight. Changing your exposure means you stop booking the kind of plans that collapse if they run late, so your evening no longer depends on a habit you cannot control. The option that does not exist, however many times you try it, is rewiring another adult's relationship with a clock from the outside. Early or Late, Never on Time walks through both moves in detail, matched against the specific profile you are dealing with, and pairs well with MYMOONOVA's free DISC profile if you want to know which one you are managing. If the pattern you are up against reads as quiet payback rather than plain disorganization, the signs of passive-aggressive behavior are worth checking next, and the same naming technique above works even better once you have read how to deliver a hard sentence without it backfiring.