Skipping or Guessing

You should try to not leave any question blank.

And you should plan on not being in a situation where you have 5 questions left and 1 minute.

Have a timing strategy that keeps you basically on pace. If you have to guess on one or two at the very end? Not ideal, but you don't want to have to rush guess five. It's just too many (though...again, better than leaving blank).

Whenever I find myself with more questions than time (e.g. 2 minutes for two questions), I usually dedicate full time to one of the questions and guess quickly on the other. I find that 100% on 50% of the questions is better than 50% on 100% of the questions, in such a case. You have a better chance of getting one of the questions right with full investment on one. Half investment just doesn't quite cut it.

This is actually a bit of a complicated topic - the optimal strategy depends on a lot of things, including your ability level, and the number of questions you expect you'll need to guess quickly at just to finish on time. In general, the higher your level, the more important it is to finish the section, even if that means guessing randomly to do so. For a below-average test taker, though, it's actually worse to guess randomly at the end than to leave unfinished questions 'blank' most of the time. Assuming you're Q40+ and V30+, you should finish each section no matter how you need to do it. Leaving guesses to the end of the section isn't all that bad, but it's much better (this is easy to do in Quant, hard to do in Verbal) to guess quickly, if you know you will absolutely need to guess, at very hard-looking questions in the middle of the test, rather than guess at the end. Guesses at very hard questions aren't going to hurt you much at all, but guesses at the end can hurt if an easier question happens to show up and you don't have time to answer it properly.

I agree with Reed's comment above about rushing. WIth two minutes left, and two questions to go, it's much better to invest almost the full two minutes in one question, and guess almost randomly at the other, than it is to rush both. Most people spending one minute per question don't do much better than they would guessing randomly anyway. So if you have two minutes to go, and two questions left, or four minutes to go and four questions left, glance at the question in front of you, and quickly decide "I can probably do this" or "I'm not sure I can do this". If you think you can solve, invest the time and guess later, and if you're not sure, guess now and invest your time in the next question, or the one after that. But in Quant in particular, ideally you make any guesses you know you need to make at hard questions in the middle of the test, rather than at the end.

And don't worry about guessing at consecutive questions - if you get two hard questions in a row, and need to guess at both of them, that won't hurt you any more than guessing at two hard questions that are spaced out in the test. The fact that the questions are consecutive is irrelevant. It's question difficulty that matters.

You ask a very good question. I agree with some of the points already mentioned. So, in the scenario where you have 4 questions left, and only two minutes, spend about a minute 30 seconds on one of the questions and then guess on the remaining 3 so that you get the answers in before your test ends.

However, I think the other point here is that you want to get to a place where you do not have to guess on 4 to 5 questions at the end of the quant or verbal section, so if you need any further advice regarding timing, feel free to reach out.

Good luck with your GMAT!