Ans.1. We know that friction is the opposing force which results from the adhesion&cohesion property between the materials at the molecular level. We also know that friction also depend upon the nature of the surfaces of the materials on which it is applied. Hence, when we use different types of surfaces, obviously there will be various 'time taken' as well.
Ans.2. Ultimately, we can conclude or we can say that it is a type of proof that friction also depend upon the nature of the surfaces of the objects.