Hundreds of romance/harem authors are just panicking right now, like they can do that before chapter 50.
HoriMiya did it in the 20s of chapter count, as well. Followed relatively shortly by their first kiss, then first time, all within the next 10-15 chapters after officially starting their relationship. Speedrunning through the bases/ABCs. Then it more or less defaulted to a slice-of-life story for most of the rest of the manga's run, with some minor revelations and movements in side-character relationships.
But yeah, harems? Never. Why would they ever go that quick? Gotta keep the status quo for that shit as much as possible. Only exception, I feel, was Nisekoi, where there really were just two 'competitors', of sorts. Everybody else had no hope going in, and most of them even knew that because they'd sacrifice their own love for the ones they were connected to that were the legitimate options. And even among those two 'competitors', I felt like it was a foregone conclusion from very early on that one was a hope and a prayer for a return to a quiet life, and the other was the real love interest that had legitimate character and relationship growth to look forward to. ... but it still waited until the very end to confirm which one was which through confessions, even If I already could read where things were going long before then (not that that's a bad thing).
Another exception on the 'slow to confess/start dating' topic is ToniKawa, where the whole premise is about the main couple going from strangers to newlyweds virtually immediately and all the diabetes-inducing firsts they have as a married couple instead of just boyfriend and girlfriend, and how that changes the dynamics of those moments. Talk about a speed-run to commitment.
There's two other examples of a couple getting together early in a series, but they're series that are mainly supernatural mysteries, not romances, so... I guess that would make for an exception, since the active relationship is meant to be sort of an ongoing thing while mysteries are solved and problems resolved.