not the OP you replied to, but someone else who loves the Drawing on the Right Side of the Brain book.

I think 5 days is ambitious. but a lot of what the exercises are doing is training you to see a different way. so it's not impossible.

someone neurodivergent may struggle to get what the exercises are trying to teach or to reach the point they're aiming for, so it might take them longer. those more inclined to pick it up faster probably aren't going to need the exercises in the book; it's already natural to them.

as we grow up, we learn "this is what a tree looks like, this is a dog looks like, this is what a car looks like", etc etc. the way we see a new car then goes through that filter of "this is what a car looks like". those filters are great for quickly identifying things and generally being a human in the world, so you don't get hit by a car while you're still figuring out if it is a car.

but those filters get in the way of drawing accurately. your eyes aren't literally filtering anything; that's all in your brain. so you need to learn to stop that part of your brain when you draw. that's the biggest part of being able to draw decently. the rest is technical skill you get with practice.

I'd still recommend the original OP look for an artist collaborator, since children's books need the illustrations to be as strong as the writing. there's no way to get there in just 5 days.

One possible interpretation is that autistic individuals can sometimes tend to go a bit overboard when finding a new hobby. We will sometimes find a new topic so engaging that we develop a "special interest" in it and spend days/weeks delving into every possible piece of information and niche knowledge available about that topic, considering all the implications and what-ifs and following all the informational leads.

Spending merely the minimum time required (which in this example is apparently 5 days) to get proficient is harder to estimate because an autist may instead need to spend weeks learning everything. Or, they might not.

Before cheap, ubiquitous photographic reproduction, drawing was taught to people as a skill.

You might not be the next Gary Larsen (I'm no dillitente) but I bet if you tried you could become a good illustrator.

Having said that, you still have to learn inking, coloring, etc.

Just wanted to say I think most people can learn the skill in the same way most people can learn to write a rhetorical essay or do arithmetic.

Edit: not trivializing your issues, friend, just offering encouragment!