how come phrase,'on eleventh hour' came into use?

Answer 1

As others have suggested, in the first century Roman Empire the day had 12 hours, counting from sunrise to sunset. The 'eleventh hour' would be the last hour before sunset -- and more importantly, the last hour in which outdoor WORK could be finished.

The expression "the eleventh hour" comes into English from Jesus' usage of the phrase in a parable about a man who went out all through the day to hire workers to work in his vineyard (found in Matthew 20:1 etc) . Of the last group Jesus says:

(Matthew 20: 6) "About the eleventh hour he went out and found still others standing around. He asked them, `Why have you been standing here all day long doing nothing?'"

(In verse 9 we discover that those hired "at the eleventh hour" were paid a full days wages. . . which upsets those who worked the entire day and are paid the same amount, for which they had agreed to work.)

Answer 2

Most people get it out of the bible, (which referred to the working hours as but it has become as katlvr125 stated)
Now it's a slang term just indicating the last minute, or when the end of something is comming soon.

Answer 3

back in ancient times when the men would work 12 hours while the sun was up--the 11th hour was right before they got off work

Answer 4

It means at the last time