Hot take: I feel like the 100 days thing is supposed to highlight how abruptly things can happen, life can change and so forth. It made sense in Croc since the overall theme was to cherish each individual day (and he highlighted that by doing one day per day) but you could just as easily have a manga like this that ends in 100 days but only "spans" about a month or so.
People need to stop strictly following the "one day per day" rule when it doesn't make sense. Like how it doesn't here. Hata just needs to bail completely on it.