The Mandarin question phrase for "what time” is shénme shíhou, made up of four characters: 甚麼時候. The first two characters 甚麼 (shénme) mean "what” and the last two characters 時候 (shíhou) mean “time,” or “length of time.”
Examples of Shenme Shihou

    Nǐ shénme shíhou qù Běijīng?
    你甚麼時候去北京?
    你什么时候去北京?
    When are you going to Beijing?

    Tā shénme shíhou yào lái?
    他甚麼時候要來?
    他什么时候要来?
    When is he coming?