Did SD last year, and I ran out of time. You certainly are on a strict limit, but running out of time is not the worst thing that can happen (I left 5 marks blank, still got a 43). I went through ABC, that was a mistake, I should have left A for last, so I could just tick all the MC when I came short of time.
The worst thing you can do is waste time on a question. I did that way too much, looking over MC for too long. And ugh, that question with the magical "not-very-large" 80GB software some numb-nuts wanted to fit onto a DVD, plus data files, I read that over for 5 minutes trying to figure out what I was misreading, and ended up just leaving that question... just keep moving through the exam, and make sure you attempt the questions you think you can do. Leaving stuff blank to work on questions you're more confident with is fine.