How long does it take to walk 9 kilometres?

It depends on how fast you walk. At a moderate walking speed of 4.5 to 5 kph, it would take about 2 hours. At a very brisk speed of 6 to 6.5 kph, it would take about 1.5 hours.
Walking speed for an adult may depend on a number of factors. Walking speeds are normally calculated at about 5 kms per hour, so in round figures, about 2 hours