whenの原義は「いつ」
〈疑問副詞〉
When is your work going to start?
君の仕事はいつ始まりますか？
When can I see you again?
いつまたあなたに会えるの？
When did you go to Nara for the first time?
奈良へ初めて行ったのはいつですか？
When is this program going to finish?
この番組はいつ終わるの？
〈疑問代名詞〉
Until when will you stay here?
いつまでここにいますか？
Since when have you stopped smoking?
いつからタバコをやめていますか？
【解説】
whenの疑問代名詞の疑問文の作り方
Will you stay here until［いつ］？
↓
Until when will you stay here?
Have you stopped smoking since［いつ］？
↓
Since when have you stopped smoking?
