Level Range of Dragon of Icespire Peak

I am planning to run a introductory campaign with the scenario ‘Dragon of Icespire Peak’, and I would like to estimate how long it will going to take. However, there is no where in the book written about the level range of this scenario, unless I have miss some phrases.

Can someone tell me what is the level range and how long the campaign would take assuming playing it once a week for about 4 to 5 hours each.