The hour unit used to tell time (as in 'o'clock'); used after numbers to indicate a specific hour (〜ji).
会議は午後3時に始まります。
The meeting starts at 3:00 PM.
朝6時にジョギングをします。
I go jogging at 6 o'clock in the morning.
今何時ですか？—11時です。
What time is it now? — It's 11 o'clock.
授業は毎週月曜の2時からです。
The class is every Monday from 2:00.
Used after nouns to mean 'time of/when/during' (as in 'in case of ...'), often appearing in compounds like 緊急時 (in an emergency).
緊急時にはこのボタンを押してください。
In an emergency, please press this button.
故障時の連絡先を確認しておいてください。
Please check the contact to call in case of a malfunction.
災害時の避難場所を地図で確かめた。
I checked the evacuation sites on the map for disasters.
出張時は必ず上司に連絡すること。
Be sure to inform your boss when you're on a business trip.