Just for the record, my friend, the word "passado" is a noun, a verb and an adjective in Portuguese language.
Although in English, the word "past" is also a preposition, I wouldn't use it this way.
I believe it is not quite common.
I would rewrite the sentence with the preposition after
, which is also a conjuction.
1) I’m going out after
the program finishes. = Vou sair depois que
acabar o programa.
2) She run the tests after
she decided to use the new platform. = Ela executou os testes após
decidir usar a nova plataforma.
The adverbs afterwards
would help you.
You should read the articles:
I hope you find it interesting.