In terms of timing, I think one of the biggest contributors I've seen to people spending too much time on a passage is getting stuck on one or two sentences that don't make sense or are hard to follow. When you encounter these, just skim them and move on. Once you finish the passage and have a full picture of the passage, go back to those 1-2 sentences and read them again - once they're put in context, they tend to make a lot more sense.
For the issue with the 2 remaining questions, one of the hardest things about CARS is that they love to throw in an answer that seems absolutely fantastic - it agrees with everything the author said, seems right in line with the main point of the passage, etc. This is usually the wrong answer - the reason that it sounds so good is because it's actually taking the author's opinion too far and either applying it to a situation that the author didn't address or giving too extreme of an opinion. As humans, we love making things black and white, so when presented with a polarizing answer, we're naturally inclined to think that's correct. Unfortunately, in nearly every CARS passage you'll encounter, the author will be far from polarized, they'll sit just slightly off of center on whatever issue they're discussing. Whenever you narrow down the possible answers to two, look at those two and try to identify which one either applies to a situation not directly addressed by the author or trends towards a polarized view. For example, if you're reading a passage about the unaffordability of healthcare and the author discusses the societal harms of unaffordable healthcare, you might narrow down a question about what the author would be most likely to recommend to policymakers to two choices: 1. Develop a free healthcare system to relieve the societal burden of unaffordable healthcare, and 2. Incentivize hospitals to host free walk-in clinics on a regular basis. Of these two, the least extreme is the most likely answer, which in this case would be 2.
For the definitions, instead of trying to identify the concrete definition/meaning of a word or quote, focus on the context surrounding it - what is the author trying to achieve by using that word/sentence? This will usually provide a more correct answer than trying to puzzle out the meaning of the word/sentence itself.
Finally, for questions about what would undermine an author's argument, make a quick mental note of what the overarching point of the passage was. Then, when looking through the answer choices, approach it from the direction of (sorry in advance, Trump supporters) "if I read this answer choice to Trump and then show him the article, would he call the author an idiot?". What I mean by that is, look at the answer choices for the one that, if universally true and known, someone with absolutely no background in that field would think that the author was an idiot for disagreeing with it.
