That is really short for the amount of information we've got on one of the main heroines of whom we knew basically nothing prior to these 3 months, and also her place in the story, and it might as well turn out that she is the true protagonist, and Hikari was merely a decoy.
Also real life months are irrelevant. The way I read this manga is as follows: I see a new chapter notification in MangaDex, I read the chapter, I participate in these fine discussions - and then I move on and do something else, like read another manga or do IRL stuff or whatever. Until a new chapter comes in two weeks, which as of recently contains a lot of new content to discuss, speculate about and reflect on. That's how I read the first 20 chapters (expect the speculating and discussing part, because there was no reason to), and that's how I read the following 8.
If the story had followed up on chapter 21 without these 7 chapters of context on Yami, most of us would've been of much different opinion on the events and its participants. Even still, we do not know why Yami considers or considered Hikari her "best friend", and more importantly, why did she and Yuu break up, which may further change our opinions on the past and following events.
Well I am trying and failing to get people to explain what do they mean by "pacing", and what exactly is the issue with pacing in this manga. Like, assuming that we have the fully completed manga on our hands and we have the ability to read it in one go, and some arcs take tad too long, or they skip too much stuff instead and go for the conclusion prematurely - is that pacing? Or is it when we read the manga as the chapters come out, and we feel like they are not coming quickly enough - is that pacing? Those are two different kinds of "pacing", and I think the latter one is a non-issue, and is not a quality of the manga itself.
@noleafclover75 refused to engage with me further, maybe you would? Because so far, it seems to me "pacing" has been used as a "gotcha" criticism the way people use "show don't tell" like it means something by itself and does not require any further elaboration.