Not always - there are many, like bom, último, primeiro, etc., that come before. And other can go either before or after, depending on the meaning.
Why not "dia ultimo"?
"último" should always come before the noun.
Why is the translation "Amanhã é meu dia último" rejected ? It might not be the best way but it is still valid.
"dia último" is not correct.
Can you have "meu dia final"?
No. A native speaker would not use "dia final".