I read through the notes 4 times total. First time took the longest for me. You don't necessarily need to read it 4 times if you really understand the material after reading it once or twice (although i think you should read it AT LEAST 3 times if you want 21+). There are definitely some parts that are more than what you need to know. I think reading through this notes make the DAT destroyer MUCH easier to approach. Some questions are basically word for word in the notes already. Overall, it took me about the same time to go through the notes and do the DAT destroyer ONCE compare to don't read the notes and do the DAT destroyer multiple times. If you just started, i recommend reading 2 chapters a day. If you have some bio background, you can do 3-4 chapters a day. It can vary though because some chapters are long and some are really short.