At an unearthly hour
Definition 1 of 1
Pro Tip 1/3Not Literal
The phrase doesn't specify an exact time but suggests it's a time when people usually sleep. 
I heard a noise at an unearthly hour, but no one was there.
Pro Tip 2/3Negative Connotation
It often implies inconvenience or discomfort due to the abnormal timing. 
She was not happy to start her journey at an unearthly hour.
Pro Tip 3/3Idiomatic Usage
Used in casual contexts, not suitable for formal writing unless it's a narrative. 
We sneak out of the house at an unearthly hour for the trip.