多少时间duō shǎo shí jiān (= how long?; lit.: how much, little time, room),

多长时间duō cháng shí jiān? (= how long?; lit.: how much, little, long, time),

多久duō jiǔ?" (= how long?; lit.: how much, long time)

With these words one asks about the duration of an event. Please note that information about time comes at the end of a sentence and therefore also phrases which ask for the duration.