Learn Spanish (Latin America): Hacía tres días que el superviviente dormía en la orilla. - The survivor had been sleeping on the shore for three days.

In Spanish, when an action started in the past and was still ongoing at a specific past moment in a narrative, we use the imperfect tense. The structure hacía + time + que + imperfect (like dormía) translates to 'had been doing an action for an amount of time' in English. Using a past perfect like había dormido would mean he had already finished sleeping before our story's reference point.

Do I have to start the sentence with Hacía tres días que? Can I put the time expression at the end?

You can put the time expression at the end, but you must drop the word que. The sentence would become: El superviviente dormía en la orilla hacía tres días. Both versions mean the exact same thing, but starting with Hacía places slightly more emphasis on the duration of the action.

Since superviviente ends in '-e', is it always a masculine noun?

No, superviviente is an invariable noun, meaning the word itself doesn't change gender endings, but the article tells you the person's gender. Here we know the survivor is a man because of el superviviente. If the survivor were a woman, the sentence would use la superviviente.

Could I use the verb llevar to express this same idea?