at any time; at any moment
Emphasizes that something could happen at any moment, often with a sense of urgency or unpredictability. Used in warnings or when describing a situation that may change suddenly.
地震はいつ何時起こるかわからない。
An earthquake could happen at any time.
彼はいつ何時倒れてもおかしくない状態だ。
He is in a condition where he could collapse at any moment.
when; at what moment
More emphatic than いつ alone; often used in rhetorical questions or to express impatience, demanding a specific time. Can sound pressing or dramatic.
いつ何時になったら準備ができるんだ？
When on earth will you be ready?
いつ何時まで待てばいいのか教えてくれ。
Tell me until when exactly I should wait.