A nonspecific time in the late night / early morning hours when most people are asleep, and it would be considered "ridiculous" to be awake.
The hours that different people believe fall in this category vary depending on whether one is an early bird or a night owl, but most people would consider any time between 2 AM - 6 AM to be ridiculous o'clock. If you believe midnight is ridiculous o'clock, this is a sign you are getting old. And if you think 8 AM is ridiculous o'clock, you are most likely a college student.
1. Senior citizens eat dinner at 4 PM and go to bed at 7 PM (after watching the 6 PM news) because they wake up at ridiculous o'clock.
2. John slept until noon because last night he stayed at the bar until last call and got home at ridiculous o'clock.