As someone with ADHD I feel you so much. It will be a miracle if I find the right combo of strategies to become an "actual adult". Willpower is a myth for me, I'm quite literally internally screaming at myself and fully ready to go on with an activity/task but my body just won't budge. This has severely affected my ability to draw, and even though I have a motivator/deadline of having to reach a certain skill level before I can reapply for an illustration/concept art master's course (wasn't accepted this year), it's been more stressful than motivating because I have to force myself a lot to give in the "time and effort" and I have the constant fear of not making it in time.

Now, regarding Drawabox, I jumped right into it as it was a solution to half of what the uni didn't accept me for, plus it's great to do these exercises as there's minimal space for perfectionism and forcing me to focus on creating a harmony between my eyes, hands and brain during the act of drawing, it's an interesting sensation too. I've been at it for almost 3 months and just started Lesson 2. I can't say if that's fast or not but I had to be very careful to avoid burnout and quitting, so it's the fastest I can (almost healthily) manage. I've been going through a lot of problems regarding initiating and maintaining focus on and off since the last 70 boxes of the 250 Boxes challenge, trying to implement new strategies like taking short breaks every 30 minutes, stretching/moving about more, having 1 art rest day a week (2 if it won't be enough, still testing). One day I can do 8 boxes in like 45 minutes along with doing a landscape speedpaint (art I enjoy/am the strongest at) and human anatomy practice (my weakest point), and the next day I take 2 hours to do 4 boxes because I keep zoning out and have to call it a day so as not to sabotage a potential following good day. It's the huge differences in my performance that complicate my attempts to smoothe them out.

I don't know if you have ADHD as well or not but these strategies may help either way. I also recommend warming up your body with exercise and stretches before each drawing session (you'll be more relaxed, your body will be more ready and you'll prevent arm injuries like wrist tendinitis or carpal tunnels, I've been dealing with mine for years and this helps keep it at bay). With the 50/50 rule, I mention drawing something I enjoy AND I'm good/best at. That way you can increase some potentially lost confidence, you get to further improve in an area you're more skilled at, and/or experiment and play around. For example, with my 1hr landscape speedpaints, they're still mostly studies of my photos but I try to push/experiment with the colors/composition and find ways to draw trees/rocks/grass etc. in a faster/more fun/dynamic way. So far, even the less successful landscapes are still good enough. Plus I get to implement my improved line-making and my starting sense of feeling perspective. To mention some other art activities I've done with DaB - life object studies (great to test out DaB knowledge), 3D printed human skull studies (good balance between object/anatomy for me so it's not a weakness anymore), 2min gestures (from photos, digitally), sketching my partner/pet cat/animals at the zoo (to practice anatomy from life), animal studies and so far that's it during the time I've been doing DaB. I went through months of not doing any art before so I'm keeping the art on the shorter end of time taking. I really want to do illustrations, ref/pose sheets and other projects but there's a much higher chance of burning out and I have to take it slow.

Nine months ago I was trying to find a way to make drawing fun too, and fully focus on that. What gave me a spark was grabbing the most feared/lowest quality art supplies I had (none were erasable and they are meant for generally quicker work I'd say), and do studies with them or doodle from imagination. Knowing how bad I am with the media, my perfectionism didn't appear or it was minimal, and so I had much more space to enjoy it and go through the process of figuring the media out in a more explorative way. Thanks to this, I am now comfortable with colored ballpoint pens, colored pencils and those cheap thin markers you find in a supermarket. So even if I'm still struggling with making art fun long-term, I have more options to choose from.

In your place I'd give DaB a go but try to be extra aware of your ability to go through it and slow down/take a break when it starts getting bad (I don't know how you behave in that case, but for me it's the fact I can't focus after trying for over an hour, I'm slow, restless etc.) and try it later in the day or the next one, or just spend the rest of the day on more fun drawing activities if it's just DaB that's hard to keep going with. Also expect break days going for more than a day, or even a week, it's still miles better than not drawing for months or years, and healthier. Oh and if you have a good/productive art day, don't be like me and use it to the max and burn out for who knows how long haha.

I hope this helps or gives you some insight, and I hope you'll find a way that works for you longterm, a way that balances out the skill building and enjoyment of drawing.