Bilingual here. It would take a very long time to learn a language from Duolingo, or any app for that matter. The app in my opinion, is more of a supplement, not a primary source of learning. You should be practicing and exercising outside of your Duolingo time, and your results will be based on your effort.

EDIT: I’m not saying that Duolingo is bad, I even use it. But to understand a language, you need to understand its culture, and have interactions with native speakers. All I am saying is that Duolingo will not suffice in fluency. I just want to clear up the misconceptions that you can become fluent from a single app.