Mangaplus doesn't have as good a reader as... well, any pirate site. NONE of the official ones do, because they're all based on the Japanese official readers. It's baffling that they continue to follow that model, though, than try and imitate the system that the English-speaking world has been using since the Onemanga days.
That said, just like Summer Time Rendering and Tis Time for Torture, Princess (and others) it looks like Hokkaido Gals are Super Adorable will have all its chapters free (instead of only the most recent 3 like the Weekly Shonen Jump titles). As for catching up, it depends on how fast they release 'em. Two are up right now, if they do 2 more per week that's just 4 months, plus 3 more months to cover the chapters that will be released during the period of catch-up.
In any case, thanks for translating it to this point!