Well, he took power between 1929 and 1930, although his dictatorship only went official in 1933 as "Estado Novo" (what a "great" year that was, right? ), so it would be accurate to say that we had 41 years of his regime.
And although the dictatorship only went over in 1974 with our own liberal revolution (with tanks and soldiers but very peaceful, I think only 1 or 2 deaths, very unusual for a revolution..), Salazar died in 1970, being replaced by his successor, Marcelo Caetano.
Fun fact: Others dictators died through suicide, or were murdered, or died naturally of old age. Not Salazar. He died after falling off a chair and hitting his head on the floor