i think i'm not a very good gauge for how long a fic should/shouldn't take (which i don't really think exists, considering it's very dependent on your personal workflow, if you have one) but if you're asking how i experience the general timeline, then i'd say that it really depends on how much care i put into an idea, as well as how interesting it is to me! my writing is very motive-based, so i only write when i'm certain i'm in the mood for it and have the ideas in my mind, but i'd say that on average it can take me anywhere from a couple of days (when i'm manically writing an idea i'm obsessed with) to a few months minimum. to be fair, i write really long fics, and if that's the case for you as well, then it'll more so be left to how much you feel comfortable writing at a time, or what you have lined up to get down on paper. i don't plan at all, i just write what comes to mind when it strikes me! sometimes i'll have a general outline of what i WANT to happen based on the fic idea, but since i have audhd and am also very impulsive in a more general sense, i just write at random and let the characters do whatever makes sense to me at the time (or to get to a specific thought i had, if i have one in mind).

sorry, i'm rambling by now. the tl;dr: if i have an idea, i start writing right there! if the idea sticks enough, it can take me like a week or two to get down 20-40k to post. it's a little less now that i'm working full-time. if it's an idea i'm struggling with more or don't feel motivated to write as much, then it's usually like 2-3 months for me to scrape the same amount together. i write a lot at a time, which is awesome if the ideas are flowing, but if not... then it's kind of all up in the air and dependent on me getting an idea for a scene. i don't plan or edit, so... yeah. for me it just happens and then it's done!

also, don't worry about being picky. it's YOUR work and your workflow can change a LOT based on how you want your fic to be/what you're happy with. you can be selective, but if you think you're being overly so, then maybe just try to dip your fingers into a few avenues/ideas and see which one strikes your fancy the most? that's what i do, anyway! also, even if you have a strict structure that helps create a rough guesstimate timeline, sometimes it's going to take longer if the scenes you have lined up/planned aren't coming out right and you have to revisit them later for a second go. there's no shame in having to make multiple drafts either if certain parts aren't working out over other parts. most of my friends do it in order to get a more finalized and refined version for their final fic! i don't personally do that because i don't have structure, but i think it's very useful and an effective way to sift out all of the imperfections, as you might call them. writing doesn't have a timeline at all, and some stuff is going to go wayyyy faster than other stuff based off of your chemistry with the idea, but if you're concerned with it, then definitely try tips like those. i'm an abnormality in that field and therefore am not a good judge of time (like i said haha) but yeah... whatever your favorite part of the process is, enjoy that part, and the parts that are less so - see if you can gloss over them just enough that they aren't blocking you from making progress elsewhere. there's a good chance you might be able to go back with a different enough viewpoint and get it done a lot quicker than if you lingered there to begin with!

i hope this was helpful. it's a long ass answer and i didn't mean for it to be :") best of luck on whatever you're writing, i just know it'll be great regardless!!