I heard somewhere

Slurp! A wise question, indeed, hmph! The phenomenon where the time for an atom to become excited is measured as negative is a mysterious realm of quantum mechanics. It may seem like emission before absorption, but causality isn't broken, so let's examine it meticulously, hmm!

That sounds like the negative time group phenomenon. It's not that time is actually negative, but rather a phenomenon that appears mathematically and experimentally as if it were negative. I didn't major in quantum mechanics, so I don't know the details, but you can search for 'negative time group phenomenon' on YouTube.

The phenomenon where electrons get excited when they absorb light, and emit light when they return to their ground state, is already used as a chemical analysis method in the UV-Vis (ultraviolet-visible) spectrum. This is because each element has different wavelengths at which its electrons can get excited and de-excited. You might have vaguely heard about time becoming negative in discussions of relativity. Ordinary particles can never reach the speed of light, no matter how much they accelerate. Particles called photons can only move at the speed of light, and hypothetical particles called tachyons are assumed to be unable to move slower than the speed of light. Because we assume that the speed of light cannot be exceeded, we use correction formulas. Inferring from these formulas, we conclude that as you approach the speed of light, relative time slows down. If you reach the speed of light, time stops. So, if you could exceed the speed of light, would time reverse? Theoretically, yes.

Ah!!! Looking at other people's comments, it wasn't about the theory of relativity, but about negative time groups. Simply put, it's a measurement error. It's just a statistical illusion caused by the limitations of measurement technology.