value of time

What is the definition and value of time?
How does one measure it?
Is it part of eternity?
Do we have standards which will help us to have a concrete notion of time?

Read the Following:

To know the value of 1 year ask a student who has failed his exams.
To know the value of 1 month ask a mother who has delivered a premature baby.
To know value of 1 minute ask a passenger who has just missed the train.
To know the value of 1 second ask a person who has just escaped an accident.
To know the value of 1 millisecond ask the athlete who stood second in the olympics.