On visitor\'s visa, how late can one travel?

[Himanshu Gupta]

My parents got a 10 year visa in June 01. They have not made a trip so far. A friend of mine told me that there\'s a time limit on the first trip that they make i.e. they have to make their first trip within a certain duration of obtaining their visa or else it stands cancelled. Could some one clarify on this?
Thanks,
Himanshu