1. 0 - unless you count 15 minutes of adding stuff about different types of numbers into my calculator
2. Basically, I would finish in 15-20 minutes. I would spend about 20 seconds on easy, 40 seconds on medium, and 1-3 minutes on hard. One hard problem usually requires 5 minutes or more of thought for me. I'd use whatever time I had left to go back to the very beginning and check answers.
3. When I read the problem, I'm usually already writing down numbers. After I read the problem, I know exactly what to do, without even thinking. It's really hard to explain. Usually I recognize the type of problem pretty fast. I always like to write down every number and make sure I know exactly what it is. I don't look at the answers until after I get mine. If it's wrong, I go back and reread the question really slowly. If it is a medium or hard problem, I'm usually aware of traps and make sure I underline key words (like radius vs. diameter etc). I'm basically "in the zone" and it becomes like a routine, except when I get to the one hard problem that throws me off. Oh yeah, and if it's about some kind of shape, I ALWAYS draw it, no matter how easy the problem is.