I think I'm going to be asking this question quite a lot after a few caipirinhas in Brazil.
"Is it Saturday or Sunday?" is common in English, though "Is it Saturday or Sunday today?" is also common. "Is today Saturday or Sunday?" is common, while "Is Saturday or Sunday" is not correct.
While "Is it Saturday or Sunday today?" may be common in spoken English, Libor is correct in that, because the pronoun "it" already exists in the sentence to replace "today," the word "today" is pretty inefficient/redundant.
Sometimes it is necessary to say today, because "it" is actually ambiguous. For example, someone just reminded me about an event I'm going to this week. I couldn't remember the day the event would be, so asked "Is it Sunday?" In that case, "it" does not refer to "today" at all.
You use either "today" or "it". Using both is redundant because "it" is a pronoun referring to "today".
Also how come there's no inflection in this question? Every language has a particular inflection when asking a question. The recording shows none.
The sound is not very good. There should be a question intonation, but there's really no changes in words or their order when asking in Portuguese.