by night meaning

• [American slang]
  Go to by day

• at night:    [American slang]du ...
• night:    Noun: night & ...
• of a night:     or of nights1. In ...

Examples

1. the fugitives traveled by night and rested by day.
2. she sleeps by day and works by night.
3. the enemy fled in disorder by night.
4. the robbers fled by night.
5. by night time, he was ill.