Depends on how strong you are in math. When I first got my hands on the math destroyer, it took me literally 1-2 hrs to go through 1-2 tests. Maybe longer. I had no idea how to do any of the math. Plus math is my weakest subject. However, that being said, I got used to the math tests/questions, and I could finish the QR within the alloted time and get somewhat reasonable scores.
On the DAT, the math portion was earily similar to the Math Destroyer. I ended up with an 18 on that section. I'm convinced if I didn't practice with Math Destroyer that I would get below 17 which spells trouble.