Irregular times, as in You can't come home at all hours and expect your supper to be ready. The expression can also mean “late at night,” as in College students like to stay up talking until all hours. It is sometimes amplified into all hours of the day and night. [c. 1930]
The American Heritage® Idioms Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
How to use all hours in a sentence
Again, the Europeans have AWACS, but not enough crews to handle an all-hours campaign lasting months.
Then Abdullah called for one of his private secretaries to hand over his name and an all-hours royal-switchboard telephone number.