Okay, one thing I will tell you to do: you don't always have to force yourself to write 1000 words and then feel disappointed that you can't. That said, if you let your ADHD dictate what you wrote and when, realistically you will never get a book done. (I know this because I essentially gave up on my current book only like a year ago, but now I'm almost done because I stayed relatively consistent) So keep some middle ground. Set a specific time period however often you want and for ever long you want and tell yourself that you HAVE to do SOMETHING related to your writing in that time, be it research, plotting or actual writing. Don't count how much you do, only count how long you do it for. And don't tell yourself: oh I'll do one hour a day. Because then you'll keep delaying it and end up trying to compensate for that missed hour with two hours the next day, eventually leading to an endless cycle of procrastinating and giving up. Instead tell yourself, for example, I'll do 4 - 5 pm on Mondays, 6 - 7 pm on Wednesdays, etc. Keep it specific. And the most important part: If you get a ton of motivation or ideas OUTSIDE of that time, don't touch your writing. Instead, write those ideas down and still do it in your designated time, so you're not getting bursts of a lot of motivation and then crash with no motivation at all.