Whilst a full tour lasts an hour its unlikely that you would do the tour in one go as part of the attraction is that it takes you from the lower city up to the gates of the fortifications, cutting out walking up the hill.
The outbound route takes in a tour of the lower part of town before crossing the river and climbing to the fortifications
The return trip starts with a tour round the outside of the fortifications before heading back into town
A commentary in French only is provided along the way