In defence of "Till", it's a widely used English word - especially in Scotland and the North. Used since the 12th century it derives from Old Norse and is often confused with the contraction of until ('til) as it has pretty much the same meaning. My understanding is that it precedes "until" in English usage. I'd hate to think that we couldn't use it.
Till and until are both old in the language and are interchangeable as both prepositions and conjunctions: It rained till (or until) nearly midnight. The savannah remained brown and lifeless until (or till) the rains began. Till is not a shortened form of until.
I have used it all my life.
And it would seem my previous lives too:
Till has been in use in English since the 9th century; the earliest sense of the word was the same as the preposition to. It has been used as a conjunction meaning "until" since the 12th century [almost as long as Portugal has been around as a country]. Until has been in use as both a preposition and a conjunction for almost as long. Both of these words are acceptable; you may send a text to your misbehaving child stating either “U R grounded till 4ever” or “U R grounded until 4ever.”
Feira is fair. It's easier and faster not to say feira every time, but the proper way would be to say the complete sentence: second-fair, third-fair, fourth-fair....
Note: Third means terça when it's a fraction, but terceira if it's an ordinal. So it should be terceira-feira, but - maybe because of the weirdness of saying tercEIRA-fEIRA - it was reduced to terça-feira.
Because when the new system of days was set up in Braga, Portugal it was related to Easter Week (Semana Santa) and prima referred to Palm Sunday. Prima was the first day of rest (feira = no working) during Holy Week. Domingo was Easter Sunday.
Sábado comes from Sabbath which came from Jewish tradition of worship on Saturday so was considered the end of the week; hence why Sunday is considered the first day of the week, but also in Christian circles Sunday is also considered the 8th day (or day of resurrection) which is of course tied to Easter Sunday.