The Asteroid-in-Spring Hypothesis

Because there has been significant academic infighting over whose theory it is, and whether the evidence comes from a faked source.

The significance is likely more about paleontological methods of time determination than it is about what the difference of the impact would have been had it struck during another season, though that could also turn out to matter.

A massive asteroid impact is a singular event, and most especially in the realm of geology and paleontology, where the minimum timespan of concern is frequently one million years, the notion that we have reasonably postulated that specific fossil finds can be pinned to the day of the event (there's a T. Rex find that seems to have occurred on the date), and then to identify when in the year that day happened to fall (based on specimens of fish and fauna found in a deposit timed to the impact) provides methodologies which might be used to confirm (or refute) the timing both of other K-Pg boundary finds, and of paleontological / paleobiological finds more generally.

What we don't have, mind, is a speific timing of the Alvarez impact. The current estimate, based on argon dating, is "66,038,000 years ago, plus or minus 11,000 years" (<https://en.wikipedia.org/wiki/Alvarez_hypothesis#Evidence>). Though that itself is pretty remarkably precise.