What is the difference between the questions. "¿Qué hora es? and "¿A qué hora es ...?"
1. ¿Qué hora es? asks for the time and ¿A qué hora es...? asks at what time.
2. ¿Qué hora es? is used in the morning and ¿A qué hora es...? is used in the evening.
3. ¿A qué hora es..." used when you are speaking formally.
4. They are written differently, but they ask the same question.