Actually is not one day, the big mangas get released very early during the night of Thursday to Friday and the official releases are on Sunday, so is basically 2 days and half. Today i read most of Jump mangas on the Manga Plus but One Piece, nah, it hurts my soul everytime i read "Zolo", i just can't...
And to point one thing, this "higher image quality" is really debatable, there's some chapters that i read on my phone in the app that you barely gives a extra zoom and the image and texts get blurry while if i do the same with the scan version, i can zoom the hell out of it and still good.