"My house is a mess!"
"Cleaning the house was fine, but then I couldn't stop until I finished--at 5 a.m.!"
"I'm a procrastinator. Nothing gets done until the last minute."
"I meant to get something done today, but I couldn't stop checking my e-mail."
"It takes me forever to get ready in the morning!"
"I put off my homework until 2 a.m."
"I knew I should stop, but I found myself playing my three hundredth game of Solitaire anyway!"
That's executive dysfunction.
Mild-moderate ExD is what you see with ADHD. Basically, problems with planning, organization, and multi tasking. This is what can make a complex task seem insurmountable, the "I don't know where to start" feeling that keeps you procrastinating. It's a normal human experience, actually, that NTs have; only people with ADHD and autism have it a lot more, and a lot stronger. Severe executive dysfunction can make brushing your teeth into a problem that's too hard to solve, even though you know how to do it and are physically capable of it; so you have to use a reminder list or get somebody to tell you the steps while you do it. Those can be used for more complex tasks too. I have lists of steps for getting ready in the morning, for example. If you can write and follow your own lists, you've gotten over a lot of the problem.
Another problem is "inertia". I don't know if that's an official name for it. It's basically the idea that starting something or stopping something is difficult. The autistic mind (or MY autistic mind, anyway, and those of many others I've talked to) resists changes in speed and direction, just like a moving object does. Switching from task to task is difficult because you have to switch mental gears. So is starting something. It can be difficult to start taking a shower, or difficult to start writing a term paper. Stopping can be a problem too. I once stayed two hours overtime at my job, without permission, because I had not yet finished sorting the womens' shorts. I knew it was time to go, but couldn't figure out how to stop.
In other cases, it's like you've completely forgotten the concept of starting, stopping, or changing activities. That can be a problem too, and worse than knowing and not being able to figure out how. Sometimes it takes outside help to break out of those problems; other times you break out of the freeze yourself.
Sometimes inertia can be overcome by having a plan ahead of time that includes the transitions, so that you are following the plan. Your inertia works for you, because at least part of it will keep you on the task of "follow pre-arranged schedule", and that balances out the part of it that doesn't want to go through those transitions. I think my morning plan is part of the reason I can tolerate showers--it's time to take a shower, so I do; and before my sensory-based hesitance to take the shower can kick in fully, I've gotten into and out of the shower and things are OK again.
If you plan your project into your day, and you follow that plan, then you will tend to follow the plan rather than make a new one mid-step, because making a new plan is more intimidating than following an old one.
"Adherence to rigid, inflexible, nonfunctional routines" (DSM) can be a problem; but it's more of a coping skill than a direct result of autism. The solution to the problem of routines isn't to try to stop using them, but to get them to work for you. You do things for a reason. Even "nonfunctional" routines have a function.
One caution about timed schedules: They can be problematic when your actual execution of your schedule is different from the scheduled times. Let's say my schedule says, "Breakfast, 6:30 to 6:45." It doesn't take any longer than that to eat cereal, so fifteen minutes makes sense. But then I have breakfast, and I take longer than fifteen minutes--maybe I'm tired or I'm daydreaming. It's 7:00 and I finish breakfast... what now? Do the 6:45 item, "pack backpack", or do the 7:00 "drive to school"? Decisions--and suddenly the plan's off track and I have to construct a new one on the fly. Bad idea.
Better: Have a list, without times, and make it flexible enough that you will finish what you need to finish on time about 95% of the time. So my morning routine takes, at the shortest, 15 minutes, and at the longest, 45. (Still a far cry from the three hours it took pre-list.) I get up an hour before I have to leave for school, to allow for enough flex time, and fifteen minutes extra if I lie listening to the alarm clock for a while, can't find my keys, or have to scrape frost off my car. (I shouldn't lose my keys, though. Part of my getting-home routine involves putting them in a small bag I keep clipped to my backpack.)
ExD is annoying. Really annoying. However, it's possible to put into place strategies that let you use what you've got, and even take advantage of it. Just sitting back and hoping that next time you will be able to start when you want, work as long as you want, and finish when you need to, won't help much if you don't have a plan ahead of time to try to make that happen.