This simple change and the recommended fix has another issue that this post missed or dismissed as a non-issue. What if the deadline is pushed back after the email reminder is sent? Do some users rely entirely on the email reminders and might they need a followup email saying "Just kidding, actually you've got more time" - assuming you resolve that question, when the due date comes up again should you send another email? What should happen (with these daily emails) if a task is pushed back an hour without pushing it out of the 24 hr bound? What should happen if it does push it out of the 24 hr bound but just by a little bit? Should we encode some sort of grace period of ignoring the change? If a due date is scheduled and due to go out immediately should we allow a grace period for canceling it?

The technical questions behind why a change takes a long time are legion, but so are the UX changes that all need to be accounted for. In software there is no intelligent actor that can solve edge cases you missed when they come up, instead you're building a system that will handle all of those cases (maybe by occasionally crashing, granted) so user stories need to be vetted and resolved.