30 minutes – check any Chanuka howto. But why 30 minutes?
The Talmud source is one sentence about the candle lighting "Its mitzvah is from when the sun sets until the foot is gone from the marketplace." (Shabbat 21b). The time when people are no longer in the street has been determined to be about 30 minutes (by the Rif in Shabat 9b, apparently).
Now, the sentence could mean two things, a point in time when the candles should be lit, or a duration. And whenever two opinions are possible, we have both: The optimal time for candle lighting is at sunset and the minimum time the candles must burn is the time between sunset and the time people are no longer in the streets (Shulchan Aruch, Orach Chaim 672:2, Mishne Torah, Chanukah 4:5).
And (of course) there is an opinion that nowadays one should light longer than half an hour because people are out on the streets for longer (Halachipedia: How long do Chanukah candles have to be lit). But most texts I have found stay with the 30 minutes.
Happy last day of hanuka!