Time is tight in 11+ entrance exams. Multiple choice papers allow roughly 1 minute per answer and open answer roughly 1 minute per point. Any child hoping to pass a selective entrance exam needs to be in the habit of keeping one eye on the clock at all times. Start building this habit early, even if it's only on 5 questions at a time.
Make sure there's a clock on the wall and your child is building the habit of measuring where they are vs how much time they have left. Unfortunately, getting every question right doesn't matter if you only answer half the questions, and likewise spending too much time on one question that's only worth 1 point could cost you the exam.