These guys don’t understand that the speed of reading is dictated by THEM; if it takes you only 5 seconds to get through the 20 pages of the chapter, calm down, dude. Nobody is chasing you.
Besides, a manga/comic is not like a movie/series where the pace of “playback” is constant regardless of whether there is dialogue or not in the scene. A scene in a movie is going to last, say, 5 minutes with or without the dialogues, if it’s action or contemplative. In a comic book it’s obviously going to take longer to read a page with dialogue than one without. Worse still if it’s a two-page general shot with no dialogue, if you don’t go into every detail of the scene, you’ll see it for half a second and move on.
If you feel dissatisfied with how fast you read a comic book… Boy, it’s your fault.
I don’t know what Manga Plus is, but I assume that this isn’t actually complaining about the time so much as the amount of content, and using the time as a proxy.