I was there a months ago and wasn't sure until I read about it. Its going to take a while to do Destroyer in the beginning if you're doing it untimed, but it will help you get better and it will help you retain things because of the way you do it.
I did everything as the above 2 said. First time around for DAT Destroyer (GC, OC, and Bio): I would do 27-30 questions a day for oc and gc and 35 for bio, but I would try to mock the actual exam by doing 40 bio, 30 gc, and 30 oc a day. I would do the questions untimed, spend as much time as you can and try your best to get the answer as long as you believe you're doing it the right way. If you don't know then try your best to choose the right answer (there are going to be some topics you've never ever covered and that's what learning is all about. Plus you'll be noting things down that you need to work on, that you need to study more with, and how things work like a certain reaction goes this way and not that way). I would write my answers on printed excel sheets (one column for the answer and one column for any important note like a star or circle that I need to come back to this, or this looks important, or I gotta work on this, or I need to make note of this to re-learn it). After finishing a section, I would go to the answer key and check to see which ones I got right and wrong. The ones I got wrong I would mark them with a pen. Then I would write my score out of 27 or out of 35, etc. Then, I would go back to the problems and look at the ones I also got right and wrong. The ones I got right I would do the problem again to see if I had done it right (without looking at the solutions) or I would look at my scratch sheet that I had performed it on. 95% of the time though I knew what I did since I did the problem not a while ago so I would check the answer and see how it compares to how I got the answer. For example in GC if they did the calculations differently from how I did but got the same answer then I would make sure that everything worked out properly. Most of the calculations I learned from Chads so I would use his method and I'd get the same answer. If it was a non-calculation question, I'd run through the answer choices to see if there was anything important. For example if this was a conceptual question about Boiling points and melting points and there was something that I didn't know then I would note it down in my notes. I would also star that question or research on it that moment to see why that is because to me certain things need to make sense in order for me to move on. I like to have things make sense. That's for me though and it may be different for others and for you. Then after writing the necessary notes I would move on to the next. Even if I got it right I would still note things down. Sometimes the question would seem obvious but it looked very important to, which is why I would write those things down. Keep in mind it would take a long time (almost my whole day) to this everyday. I think the first time I went through DAT destroyer (oc, gc, and bio) and Math Destroyer (1 math test per day), it would literally take up my whole day because I would spend 2-3 hours doing Math destroyer untimed and for DAT Destroyer I was really bad in oc and okay in GC. All this stuff would take up my entire day. Don't forget that going through the answers, writing important notes down as you go along, and researching certain concepts would take up all my time. Sometimes I would rarely get to practice my RC by reading something nor would I be able to do some PAT practice. Its all time management though. When I started doing it for 12 hours a day, then I started getting things done in that day. The bio section I would race through, but there were some tricky questions. I am going through it a second time right now with time and obviously it doesn't take that long (because its timed), but I try to do the problems and finish them even if I run out of time just to learn it and be better at it. The second time you run through it, its all about efficiency and how quickly you can do something under pressure and that pressure is time (this is mainly for the Math section). They put this section at the end because you're drained from the entire 4.5+ hours of the test and there's time to see whether you can finish strong still and whether you can work under the pressure. Most of the math material seems really easy when you look at the big picture (its algebra, trig, geometry, and other high school math, but put into word problems, shapes, etc). The only reason why its hard and its difficult to do really well is because its timed and its the last section of the test and you feel the pressure of time. This is what I think though. If you go into that section feeling positive and cool, then I guarantee it that you'll be good. Plus you'll have all the prep you did with DAT Destroyer and Bootcamp. Also, if you are comfortable with flashcards and studying with them then by all means do it. If you studied using those in undergrad or college and you like doing it and did well with it then stay with that method. Everyone has their own way of studying and if you think that its best for you by going through certain things as flashcards, then go for it. I just kept all my stuff on a notebook and write stuff with my notes on there if anything is important, but flashcards is good too. Since I'm still going through Destroyer my second time and plan to take my DAT next month, I can't say how I did yet and I can't say my method will definitely work. Feel free to let me know if you got any questions. Good Luck!