I don't think you can skim and successfully get the main point, just my opinion! I think if you're working on timing, don't sacrifice reading time, but time answering questions. I found that when i spend thoughtful time reading the passage, trying to understand without having to reread, and staying focused, answering the questions goes by much more quickly.
It's hard to not move on to the next question without being 100% sure of our answer choice, so we tend to spend longer than needed to confirm our choice. However, if you've read the passage well enough, the "main idea" type answers are more likely to stick out. Each passage takes me between 4-5 minutes to read, and I take 3-4 minutes for questions. Try this with the CARS qpack!