"Time waits for no one."
We all have bad days, things we wish we could do again, regrets. That is the core of most time travel media, especially Japanese media. While this film most certainly adheres to those tropes and themes, it also ellaborates on those themes further. It's not just about learning to let go of the past, it's also about moving forward. Time waits for no one, so we too can't wait by looking back at the past.