The decision of the Health department of Brazil if bases on scientific data and algorithms, in case that contrary the missed period would be taking the population to one, the same of applies Portugal. One has tested of 3ª generation after becomes positive between 22º and 29º day the contact (a test of 4ª generation probably the 2 3 days more early, because it searches also stops beyond antibodies antigénio, but not yet has necessary estimates) in 95% of the cases, and practically 100% to the 45 days (six weeks). Everything what is outside of these periods is rarities. Some parameters in the laboratory exist today that help the diagnosis very and that they allow to give the possible precocious reply (Words of a ambulatorial virologista).
Countries don't have different window periods a conclusive negative test is 3 months post exposure.