A pronoun used to ask about time: 'when' or 'at what time'.
パーティーはいつ始まりますか？
When does the party start?
いつ日本に来たの？
When did you come to Japan?
宿題はいつまでに出せばいいですか？
By when should I submit the homework?
いつ終わるか分からない仕事が残っている。
There's work left that I don't know when it will finish.
Dated usage meaning 'ordinary times' or 'peacetime' (an older/formal sense).
非常事態が終わって、いつ（＝平時）の生活に戻りたい。
I want to return to ordinary life once the emergency is over.