Hi Federico!
Maybe if I translate in Spanish (very crude Cuban dialect so bear with me please!) you might get a better understanding okay?
Para el primer pulgara, usa Sesenta minutos o una hora... Entonce para el segundo plugara, usted tiene que anadir, aumentar, acrecentar, juntar, o a contribuir quince minutos nada mas!!! Ultimamente usted vas a tener Setenta y cinco minutos o una hora y Quince minutos total usando este formula describido - comprende? ;)
Translation using my own words:
For the first inch, use sixty minutes or one hour... Then for the second inch, you have to add fifteen minutes nothing more!!! Ultimately you will have Seventy-five minutes total, or One hour and Fifteen minutes total using the formula described - understand, comprehend? ;)
IMHO = In My Humble Opinion :) :) :)
Respectfully,
Henry