Why do I keep revising my work until the last minute?

Be honest with yourself about what those final rounds of edits are doing. The version an hour before the deadline is rarely better than the one from two days earlier. You are not improving the work in those last hours. You are managing your own anxiety, using the document as something to hold onto while the nerves run their course. That matters because it means the endless revising is not really about quality, and no amount of it will ever feel like enough. Anxiety does not get satisfied by one more pass. It just finds the next word to worry about. You could polish forever and still feel the same dread, because the dread was never about the work. Try setting a real finish line: this version, at this time, is done, and I will not touch it after. Then, when the urge to revise rises, sit with the discomfort instead of editing it away. The work was good enough hours ago. What needs settling is you, and revising is not how that happens.