Late light bulb shines in vain

This happens to me a lot. I come up with the perfect birthday present for someone the day before their birthday even though I've been brainstorming for weeks. I spend hours the night before class preparing my lecture but can only see exactly how best to explain a concept 5 minutes before class starts. This doesn't often happen in my illustration work, but it just did. I was tasked with coming up with cover art from scratch in under two weeks, and given free reign to conceptualize the paper. It's certainly not a demanding or even unusual timeline, it just doesn't leave as much time for brainstorming. Yesterday I submitted the image below, which I'm perfectly happy with, but today, a day before the deadline, I come up with a way better idea. Now I'm kicking myself, or at least whatever mysterious part of myself produces ideas whenever it feels like it and too often not when I'm trying really hard to make it do so. I'll just have to keep the idea in my back pocket for now.