From understanding inference, to identifying a flaw, to figuring out the intricacies of a situation, critical reasoning questions in the GRE can test you on several skills. The test here looks at a set of questions that test you on lines similar to those that you are tested on in the actual GRE test.
Many test takers completely ignore the critical reasoning section. Worse still, there are those who are unaware that something like this exists.
Understanding how these questions work and knowing the question types you might encounter in the test can be vital to scoring well in the verbal section of the test.
This is an untimed test.
In the actual GRE, all the sections are timed.