Personally I prefer it starting on Sunday, but also here with Portuguese being the main language it only makes sense to start on Sunday, Monday to Friday are called second-fair, third-fair, fourth-fair, fifth-fair, and sixth-fair. Fair as in either market or festival.
(For those that don't know, many tattoo shops have Friday 13th deals with specific flash you can get for multiples of $13 depending on complexity. The quality ones have new cute Friday 13th flash a couple of times a year and lines around the block.)