1. at what time
Usage: used in questions

1. at the time that; during the time that
2. at any time that; whenever
3. considering that; since

1. what time; which time
Usage: relative pronoun

Examples

• When did you arrive?
• I was sleeping when the phone rang.
• Call me when you get home.
• Why buy expensive clothes when cheaper ones work just as well?
• That was when I realized my mistake.
• Since when do you like jazz music?
• When angry, count to ten before speaking.