10yr. Visitor Visa - Timelimit for visiting first time

[immihelp]

My parents have been issued a visitor visa on 26th of February 2009 which expires 10 years from now and I am very thankful to immihelp.com for providing the database which was really helpful.

Now my question is:

Is there any limit as to when should they come to U.S.A after their visa is issued? How much time-lag is allowed between the issuance of visa and coming to the U.S.A., what if they are planning to come to the U.S 1 years from now?



Thanks.

[immihelp]

They can come at any time within next 10 years.