I'd say that doing 4 hours a day is definitely excessive for prelims. Perhaps once you get to study leave it's a more reasonable figure, but then again you don't go into school in those times anyway.
But, even though prelims can't be used as evidence anymore, they're still important. It's good to get used to the idea of having a bunch of exams within a relatively small timeframe, getting use to a consistent study routine (note that consistent doesn't necessarily mean a lot of study time), and even just getting used to what the exam's going to be like (I've sat prelims for National 5s and Highers so far, and it's really similar to what isitting an exam's like). Naturally, prelim papers tend to be a bit shaky (a lot of them are produced by outside companies, so there might be a few janky questions), but they're a pretty good approximation anyway. They don't "mean" anything per se, but they're still important.
And I can give some advice for a few of your subjects (the ones I've done, at least):
* For Maths, the main thing to do is to practice questions. Make sure you can identify what you need to in a question, and make sure that you can carry out procedures (e.g finding the gradient of a lin) confidently. Make sure your fundamentals (like fractions) are solid, so you won't need to worry about things like arithmetic errors.
* For English for Close Reading, it's a good idea to read some articles from reputable newspapers or websites (it's good if you can find articles on topics you're interested in), and try and think about things like word choice, sentence structure, and other similar things you normally get in close reading. For critical essays, know whatever texts you're working on (if you're got more than 1 for the prelim, don't just spend all your time on one - you could get a really nice question for the other and get stuck with bad questions for the text you like), and keep your essay structued and clear. For the Scottish Set Text, it's especially important to know how different sections (i.e different poems/short stories/parts of a play) link together, particularly when it comes to certain themes. Again, make sure you're at least comfortable with all of them.
* For Physics, get really comfortable with the questions - that's a big chunk of th paper, and they can be useful for explanations too. Fro "using your knowledge of physics" questions , you can often bring equation or item from your data sheet, which can guide your answer along quite nicely. There's normally a question where you're not expected to know the physics as well - get comfortable with drawing and interpreting graphs.
* For Chemistry, make sure you're comfortable with calculations, that you know your way around the data booklet, and that you know general groups of things (e.g halogens). Know how to work with things like molecular diagrams and tables of data as well.