'At night' usually refers to the hours of darkness when most people would be sleeping. For example, 'My sister's a hospital nurse, so she often works at night.' 'In the evening' is the last part of a person's day, usually the period between finishing a day's work and going to bed. This varies between cultures, but most people would consider 'evening' to be somewhere between 6pm and midnight.

Evening is about 5pm to 9pm Night is any time after that until the sun comes up

Thank you Richard!

Most dictionaries say that the word evening does not have a definition related to specific hours (time). Here are two definitions from a dictionary: 1 the latter part of the day and early part of the night. 2. the period from sunset to bedtime.