As for time spent reading the passage, this has a pretty broad range for me. I would take a quick look at the passage and try to get the "feel" for where it was going to determine how much time I would need to spend on it. If it was a complex experiment, for example, that required me to understand all of its components, I would spend a little more time on it. However, if the passage just seemed like one of those more background-y passages I wouldn't spend any more than a minute on it and just refer back to it as needed.