You get whatever is left over when you finish the tutorial. If you still have 10 mins remaining for the tutorial you get 10 mins of extra break time. If you have 5 mins remaining, you get 5 extra mins, etc.
No, that's only the case if you choose to look at it from that perspective. In reality, you get 45 minutes of break time. Every time you finish a section early (tutorial included), the extra time remaining in that section is added to your break time.
There is a landing screen that keeps time and where you are in the test. You hit either start next block or take a break. No taking breaks during a block
When a section ends, it automatically goes to break time (which starts ticking away). You can either go take a break, or you can go straight into the next section.