I would do the concept reviews prior to the practice problems.

If you're in a time crunch, start from the end of each section to the beginning. You don't have to do all the DS questions--unless you are feeling really insecure on these questions.

First, I'd start with a concept review for math and grammar - you actually do have to know that stuff.

Then, I'd actually recommend working from the beginning to the end, but don't do every problem if you don't have a ton of time. So, do some from the early bit, some from the middle bit, some from the end bit. It's important to build on both concepts and tactics that you learn from easier questions as the questions get harder. Often times, you can figure out how to do a harder question specifically because you've seen an easier question that touches on some of the same topics / concepts, and that helps you to figure out how to approach the harder problem.