I often find that when I try something in practice I become aware misunderstandings i have, and details that I might have missed. Of course, if you implement enough algorithms you will learn which mistakes you commonly make and start making fewer of them.
I think it is only available if you were already signed up for it. I just chose to continue with the packrat add-on for my pro account. It seems like the alternative they are now offering is only extended version history. (which would save changes for a year)
I would say that it takes about 1 second on my nexus 4. If you do it too fast the app will complain, but I find that it's actually very fast and easy to do right.
The Promise of Sleep is an okay book, but it is almost 20 years old now and it shows.
I have read both books and it is remarkable how much more we learned in the time between them.
[0]: https://www.amazon.com/Why-We-Sleep-Unlocking-Dreams/dp/1501...