You meant to do it first thing the next morning, but next morning brings its own worries. Suddenly you’ve missed something important, like an early-bird registration deadline for a trade show.
Enter the 4:55 email. Just send yourself a quick email at the end of the day reminding yourself to get this done. Or BCC yourself on an update to one of the other stakeholders. Your note will appear at the top of your in-box the next day (or at least, right under the mass of overnight emails you may have).