For Chapter 70, someone out in the discussion was talking about KW putting in clocks that show how far along the series is going. And that the clock in the flashback on Ch 70 page 8 means the series is nearly over.
Kodomo no Jikan 70 - Read Kodomo no Jikan 70 Online - Page 8
I just tripped over Chapter 54 and noticed it is the identical image, a true flashback, with the exact same time -- published a year and a half earlier. Ch 54, page 14.
Kodomo no Jikan 54 - Read Kodomo no Jikan 54 Online - Page 14