Complex sentence: During the presentation, every school is graded by the jury, and during the midday of "quarta-feira de cinzas" (Ash Wednesday) the grade gathering takes place and one school is chosen to be the winner.
Split into simpler sentences: During the presentation, every school is graded by the jury. On Ash Wednesday ("quarta-feira de cinzas") during the day, grades are gathered and and one school is named the winner.