The problem isn't with temporality or "how long it takes to 'conquer' the heroine" (in a way, that mindset is itself already flawed to begin with). The problem is how one-dimensional the female characters are. They don't feel like real humans or characters, they feel like robots inserted into the story to lust over the protagonist's d* and praise him to kingdom come.
The solution, thus, is to flesh them out more thoroughly instead of simply having them exist solely to fall for the protagonist and become part of his harem. What are their goals? Their aspirations? Often, all these are left on the wayside as the heroines unrealistically give up everything to become the protagonist's wife or concubines. Seriously? Who the hell would do that in real life? I mean, some people do, but when every single girl does it, it becomes suspect. Make them feel real. Have them chase after their own dreams and aspirations. Not every heroine has to be a super-talented genius martial artist who's the next leader of their sect or a princess from the royal family or whatever. What do they strive for? Maybe this girl wants to become a blacksmith. Have her continue becoming a blacksmith instead of her conveniently forgetting how to craft weapons when she marries the protagonist. What about that heroine who wants to set up a fashion store? Surely she'll run into troubles of her own and face competitors, and she has to overcome her own ordeals instead of having the male protagonist conveniently swoop in, beat up all the other store owners in the city and do everything for her.
Another problem is that all the heroines usually tend to be carbon copies or clones of each other. Other than background (some of which are idential - sect leader here, princess there, slave in the center, damsels in distress everywhere), they all basically say the same thing and behave the same manner. If they're not praising the protagonist for being a genius or the only man who can win their hearts, or their hero who saved them from death or whatever, they are basically just throwing themselves at him. Every single one of them. Let's face it. In reality, if a girl sees that this guy is already surrounded by girls, will she really just join in and throw herself at him? Girls, if you're here, please answer me. Will any of you ever voluntarily enter a harem and share a guy with each other? Regardless of whether there really exists such people, it makes for a bland and awful story if that's what all the girls do. Not to mention repetitive. Imagine reading the umpteenth time of girl number 7 trying to seduce the protagonist in a similar fashion as girl number 2 and 5 (I dunno, night visit or dropping in on him in a bath). You get sick of it after a while.
Then there's rape. Seriously, in what universe will a girl conveniently fall for a protagonist after he rapes her? It's a criminal insult to real victims of rape, many of whom suffer emotional and psychological damage after the ordeal. But no, these girls just recover as if nothing happened, or it was nothing more than a one night stand, or they comically explode into a murderous tantrum and try to kill the protagonist (and fail spectacularly), only to fall for him eventally. That is utter BS. It's not realistic at all. Normally they would suffer tremendous trauma after that, not the same paper-cut behavior you often see in xianxia or CEO novels. The authors clearly have not gone through the experience (and I sincerely hope they will never have to), but it's a travesty how they just belittle the psychological effects of rape. If you want such heavy themes in your story, have your character behave like a rape victim. Don't have them childishly throwing murderous tantrums, don't have them dismissing it like a one-night stand and don't have them falling for the rapist (who only gets away with it because he's the damned protagonist). Show the terrible effects of rape and how awful it is. Do not condone such criminal behavior.
It's not about chasing a girl or length of time. It's about fleshing out the heroines. They need to have their own distinct personalities, not just existing to fall in love and praise the protagonist. They need to have their own goals, dreams and aspirations. They need to respond realistically to a traumatic ordeal like rape or violence, instead of childish or indifferent behavior after the crisis. If you just got raped, your first thought wouldn't be to kill the rapist. You would be humiliated, disturbed, depressed to the point of sucide. Don't give me that crap about her being a martial artist - if that's the case, she wouldn't get raped in the first place (I'm not saying martial artists can't be raped, but the fact that she got overpowered and victimized means that she will suffer psychological damage instead of jumping after the protagonist murderously after the deed is done). Neither will you simply move on and forget about it as if it's a one-night stand.
This is not limited to xianxia alone. Particularly for Japanese light novels (and to a large extent, Chinese web novels as well), you need a legitimate reason for the girls to fall for the protagonist. Many of them just have the heroines fall for him just for breathing. A lot of the protagonists in Japanese light novels are plain, bland and boring, and the girls have no reason whatsoever to fall for him...yet they do. Using an excuse of "they are childhood friends" or "he helped her once" or "he is nice" is not enough. It's superficial, it's not deep and it's not real. Are you telling me the male protagonist is the only guy in the world who is "nice" or "helped" the heroine once? I call total BS on that. No, you need an actual, legitimate reason for them to fall for him other than because he just walks on two legs or breathes. Actual interaction matters. The beautiful student council president is never going to fall for some nobody she doesn't even talk to. Childhood friends will move on in life, make new friends and meet new guys, they are not going to get hung up on the same guy for years unless he gives them an actual reason to. That cute junior needs a valid reason to pick the male protagonist out of all the many male senpais in school. It's not just a matter of time, it's a matter of how the characters interact and developing their relationship realistically. If you want the student council president to fall for your protagonist, don't make him bland, don't give some stupid backstory of him always watching her from afar and fantastizing but never actually talking to her or interacting with her - create a scenario that allows him to stand out from all the other guys. And no, "being nice" or "helping her out" is not a sufficient scenario, because I'm pretty sure all the other guys can be nice and helped her out too. Give him something to stand out. I know protagonists tend to be self-inserts or blank canvases for readers to put themselves in his position, but that does not make for a realistic or good romance story. You need to make him stand out and give the heroine a legitimate reason to fall for him, not just hand-wave a sorry excuse of a cliche into explaining her love.
Avoid the reverse as well. Don't make your protagonist a bloody chad who's god's gift to all women and can do everything with a wave of his hand. Mary Sues are poorly written characters, and they are obnoxious to read. Most people don't want to read about a god-like protagonist who gets everything handed to him on a silver platter (this incudes the heroines). Make him work for the love and EARN it. Romance doesn't come freely. It has to be earned. Through blood, sweat and tears, and surviving ordeals together. Not by magically hand-waving the characters together or making the protagonist a Mary Sue chad.
Sorry for the long wall of text, and I know nobody will read it, so whatever.
