[quote="anonymousCentaur"][/quote]
I see your test is tomorrow; however, here are some additional thoughts.
To know when to give up on a question, you need to trust your instincts and follow your internal clock. For instance, let’s say you are 2 minutes into a question, but you know that you are on the right path; in that case, you’d want to keep going even if it would take you 3 minutes to answer, right? After all, if you have fully mastered GMAT quant, then you should be in a position to answer some questions in 30 seconds, and thus it’s OK to spend more than 2 minutes on certain problems. On the other hand, say you are 60 or 90 seconds into a problem, and you know that you are going down a rabbit hole and likely will not be able to correctly answer the question. In that case, take an educated guess and keep things moving.
So my overall point is, yes it’s OK to guess, but ensure that you are taking a strategic approach to how and when you are guessing.
Also, you may find it helpful to read this article about
Timing Strategies For a Higher GMAT Quant Score, which discusses various aspects of quant section timing, including guessing strategies, in great detail.
Good luck!