I´m reviewing telling time. Listening to pronunciation of Duas horas and Três horas, I noticed the letter “S” normally sounds like sh at the end of a word. When hearing Duas horas and Três horas, the “S” in duas and três sound like a “z”. Am I hearing it correctly? Is this because H has no sound and the next letter is a vowel? Therefore you have “S” between two vowels forming the “z” sound.