Your SAT preparation should help you develop a comfortable speed that balances the need to conserve time with the need for precision. Work too slowly, and you won't finish the section. Move too fast, and you make a lot of silly errors. There is a balance, somewhere around 70% of your top speed, that accommodates both of these concerns.
This speed will naturally develop and change throughout the test. Because easier problems are easier, you need less time to do them. The harder problems donʼt use harder concepts; they just require more effort to discern what concepts are being tested. So, harder problems will naturally take more time to solve because you make sure to read extra carefully, and even re-read problems when necessary.
Taking your time to read and act carefully does take longer than hurriedly speed-reading, but it actually saves time in the long run. When you move too fast, you donʼt retain as much information. You become more likely to overlook details and make mistakes. So, you'll need to check your answers more carefully and re-read stuff more often. In this way, moving too fast really slows you down.
Moving at an easier speed allows your brain enough time to absorb and process information. You don't have to re-read as much. You have enough time to consider details and adjust accordingly. You don't need to check your answers as carefully. In this way, slowing down allows you to move more quickly.
There are definitely situations that call for more haste. The last 2 minutes of a section, for example, would be an appropriate time to kick into a higher gear and try to move through whatever problems you have left. But that 100% speed at the end of a section is only possible if you've been chilling at around 70% for the rest of the time. Specific tools, like a coding system that allows you to quickly identify different types of problems, will help you maintain this cool 70% speed.