1A 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.
2A dated/literary sense meaning 'the usual time' or 'ordinary days'. Rarely used on its own in modern Japanese; it survives mainly as a fossilized element inside set expressions like いつになく ('unlike usual') and いつしか ('before one notices').