Продолжительность фильма - 2 часа
Никто не может предсказать продолжительность войны

Don't see any major problem with those two. Anyhow, I would rather say the second one like this:

Никто не может предсказать, как долго продлится/будет длиться война

As for the "полис", it doesn't have "продолжительность" it has "срок действия"

If you said something like "продолжительность полиса" it'd sound like you're talking about the physical length of the "полис", like it's 3 meters long. Anyhow, don't use that, it's WEIRD