に

1. Origins, structure, and basic meaning

• Structure: Add に after a specific point in time, such as a clock time.
• Basic usage: 七時に家を出ます。 sets seven o'clock as the time of leaving home.

2. Common pitfalls and similar expressions

• Time and arrival point
  • In 八時に学校に着きます。, the first に marks time and the second the arrival place. Even within one sentence, the surrounding noun and verb assign different roles.
• Relative times and durations
  • Expressions such as 今日 and 明日 normally do not take temporal に, as in 今日行きます. The three hours in 三時間勉強する are a duration rather than a point in time.