Recall from my memory, Checkpoints was mostly a collection of the past exam questions. (But with some error during their editing)
It depends on how good your memory is.
If you are the kind of person who can memorize whole year work, then do checkpoints every time you finish a chapter. And highlight the difficult ones, spend time on them, so that you can make a reference of them at the end of the year when you make your cheat sheet. (you will not be short on time)
If you are the kind of person who is bad at memorizing things (like me) , then you should start doing checkpoints at the end of the semester 1. Take note of every questions that you had difficulty with, note down the reason and the working out. Make a Cheat sheet every time you finish a chapter. (you might end up short in time)
By the end of the year, combine all cheat sheet together, and review them see whether you understand all the concepts.
Either way, you will end up with a very decent cheat sheet by the end of the year.
Lastly, after you made your overall Cheat Sheet, start doing past exams, do as much as you can. (recommended to do 20+ papers)