Examples:

• What time did you go to sleep yesterday?
• What time did you go to sleep yesterday?
• What time did you go to sleep?
• What time did you go to sleep?
• What time did you go to sleep yesterday? - Three in the morning.
• What time did you go to sleep last night? - I couldn't sleep at all!
• What time did you go to sleep last night? The shadows under your eyes are very noticeable.
• What time did you go to sleep yesterday? - Not that late. At about 10 pm.
• I can't believe how much I slept. What time is it? - It's a quarter to five in the afternoon. What time did you go to sleep?