Move at whatever pace works best for you. When I did destroyer (science only, skipped the math) with only two weeks to go before the test, I spent 3 consecutive days, one for each science. These were sort of long days - I think Bio was the worst at around 12 hours - but it was enough time to get through it all and make notes/flashcards for all the concepts I didn't know. I just studied the flashcards after that, and didn't have time to revisit the questions themselves.
I just sat down with a legal pad and went through them, 30 questions at a time (60 for bio), putting a star next to any question I didn't understand, checking answers every 30 questions, and making the flashcards/notes as I went over the answers. If you break it up into chunks like this it's easier to stay motivated, and 30 questions was a small enough chunk so that any confusion I had was still fresh in my head as I was going over the answers.
Chem and O-Chem were relatively quick, although Chem had a lot of calculations that slow you down. Bio still took forever, because there are so many more questions, but I found the Bio questions took less time as well, since there weren't a lot of calculations or mechanisms to sort through. It also helped to do this in a place with very little distraction. For me, I shut off the cell phone and internet, sat myself down on the patio with a nice cold drink and dove in.
