# of questions depends on the age of the child, the number answered correctly, the number in a row answered incorrectly, the subtest. Sometimes examiners give extra ones, for additional clinical information. It's not worth trying to figure this part out.
The duration of the test is usually between 45 minutes and an hour and a half. High-cognitive children may take longer, as they usually see more items. OTOH, some of them finish quickly, as they may be more efficient with their responses. Duration may also vary depending on how many optional subtests are administered, which depends on the referral question, and sometimes on in-test performance (if a subtest is spoiled, or the examiner wants more information on a domain).
Some of it is timed, and some of it isn't. Being thoughtful is probably more important than being super fast, but no need to bog down with tiny details, either. Much of it is like puzzles or riddles, not so much like school. Really, though, I would avoid giving any advice on testing approaches.
Mainly, get a good night's sleep, eat a balanced breakfast in the morning, and enjoy the process. This is not the kind of test that should involve prepared testing strategies, as the objective is to learn what the child's natural cognitive strategies and styles are. The examiner is likely to spend some time at the beginning helping her get comfortable with the setting. Like any other new situation, if she has questions, she should ask them, and if the rules allow the examiner to answer them, they probably will.
