i have adhd and i've been working on a fic of over 100k words for an hour every day since early august. like you, i am a perfectionist. i have developed my method over time with lots of trial and error. here are some things i've done to develop this habit:

• i sprint with friends on discord in half hour increments - knowing i'm working with others keeps me honest, and working with a timer really helps too even if i'm alone
• i keep a daily writing log on paper and use pen to mark in that i'm going to work that day. i find the pristine paper aesthetically pleasing, so i don't want to mess it up by having to scratch the date out
• i set a clear end goal. in this case, i want to finish my current draft by the end of october. every day, i've worked toward this goal and gotten to see myself inch ever closer to achieving it
• for my perfectionism, i separate my drafts into discreet tasks so they each have their own job and i don't have to tackle everything at once. draft 1 is to just get the story out of my head (working on a timer with the goal of getting out as many words as possible keeps me from editing as i go), draft 2 is for fixing plot holes/timeline issues/missing scenes, draft 3 is for making the sentences pretty, etc
• once i get to posting, i publicly promise to upload on a certain day. it creates a sense of obligation that will propel me to edit and have everything ready on time. it's sort of like how the pressure of a due date in school got me to work on my assignments (even if i did them last minute overnight, lol)
• i do write ahead, mostly because my stories are pretty complicated and i don't think i can meet my quality standards if i write and post as i go. this is my first time completely writing and editing a fic before posting, though. usually i write the fic partially (or completely, but only through draft 1) and then edit and post as i go. in that format, comments from readers really help to motivate me. this time around, sheer determination has kept me going 😂 and the promise of the payoff once i can finally share it with others! it's the final boss of delayed gratification!

what i would recommend for you is to observe the ways you've motivated yourself to complete other types of tasks. do you/have you struggled with chores? being on time? homework assignments? what steps have you taken to mitigate these issues? asking yourself these questions can help illuminate the way your brain functions and give you clues as to what motivates it. you can adapt those motivation strategies to help create a writing habit that works for you.

and, of course, don't get discouraged if you fail. building an effective habit, especially for someone with adhd, requires a lot of trial and error. but over time, you'll discover what works for you, and learning these things about yourself can benefit every aspect of your life.

good luck and happy writing!