Regardless of how much time you're spending reviewing the quant questions you do, you should probably be spending even more time on it.
The key to solving hard problems really quickly is recognition. You don't want to 'work out the solution from scratch' when you see the problem - you'll probably get it right if you're strong in Quant, but it'll take more than 2 minutes. Instead, you want to recognize bits and pieces of other problems that you've already solved before, so that you know what to do pretty much right away, as soon as you see the problem. However, since you won't see the exact same problems on the test that you've done while practicing, this is a tough skill to develop. The best way to develop it more quickly is to review every Quant problem you do in depth (including the ones you get right), and try to figure out the critical steps you had to take, and more importantly, how you knew you were supposed to take those steps.