As far as timing goes, anything that's not computer based is not going to give you an accurate representation of your timing. Time that it takes to look at your answer sheet, look back at the book, mark your answer will add up and extend a written practice section beyond the 70 minute mark.
I'll give you timing advice with this caveat: Don't worry about timing as it pertains to each individual passage. Some will be longer, some will be shorter, some will be tougher, some will be easier. No two passages are the same so you shouldn't put a set time limit on each passage. Further, if you place so much thought into clock management, you take your focus away from the test and expend energy on time management. Get used to your test taking style and perfect it within the time you're given.
My technique is to read the passage (BS, PS) first completely to understand the scope of the passage and experiments involved. When I come along a sentence that doesn't click, I'll re-read it. If it still doesn't click I'll move on. If there are listed experiments, this is where you want to understand you know what they are evaluating, why they are evaluating it and how it compares to other experiments given. This is a crucial skill you've most likely developed in your first 3 years of undergrad, whether you know it or not, so you should be able to do this fairly quickly. Next I analyze data in charts and trends in graphs to gather any information that I can quickly ascertain, ie. y increases in a linear fashion to x, this graph looks like the system displays this quality, data indicates this trend. Don't look to hard into data because you may start coming to conclusions and thinking about things that you won't be questioned on later. Eventually after you get into a habit of reading passages like this you'll find it easy because this. Writing any of this down is a waste of time because you only need to recall this information for an extremely brief moment in time. Plus, you have the highlighting tool on the CBT version of the MCAT, it serves the exact same purpose as jotting notes.
Now as you're answering questions you should be able to understand what each question is asking. You'll come across at least a question or two that will require you to do some more passage analysis, but you can take care of this on a need to basis when the particular question arises. Every question will not require an in-depth and full understanding of the material that they just presented, so don't treat the passage like it's going to.
I bolded that statement because having your own style is what is key to the MCAT. Establishing YOUR own comfort zone is what allows you to succeed. What I do works for me, it may not work for you. Adapt my methodology to what suits you, if its a carbon copy, so be it, but more likely than not it won't be. Case in point, as I was taking the MCAT today I veered from my own style. For all passages, I like to finish all the questions within a passage before moving on. I like to answer the tough questions while I'm engrossed in the subject of the passage. I did every practice test like this (each was taken in a controlled environment). Today, however, I decided to save all the real tricky questions for the end. As I got to the final review screen I clicked "Review Incomplete" and went over the test. When I was returned to that screen, I had about a minute left but still saw the "Review Incomplete" button, meaning I had missed something on my initial review. I finished that first question as time expired and don't know if there were other questions I missed. Lesson: DON'T STRAY FROM YOUR PERSONAL STYLE. Also, the "Review Incomplete"/"Review Marked" will bring you to the first question of a passage you may have multiple incomplete's in. When you press "Next", it will jump to the next passage even if you have incomplete questions remaining in the prior passage.
If you need a time for science passages, 7.5 minutes per will allow for a decent amount of review time and ample time for discretes.
