Is there a time limit on when to arrive in US

[mandal]

HI,
Is there a certain timeframe that you have to follow after getting ur Visitor VISA to arrive in US. The guy who delivred ( courier) my parents passport with thier visitor VISA said that they have to arrive in US within 45 days of getting the VISA. IS it true, if yes then where does it say so ?

Thanks

[dahlia]

No such rule. They can enter any time before their Visa expiry date