Immigrant Visa IR5: Minimum number of days entering US before Visa expires?

[nvn_gc]

Greetings,
My parents got IR5. I was just wondering if there any rule that the Immigrant must enter the US before say 30 days before the Visa expires.

USCIS mentions that:The immigrant Must enter before the immigrant visa expiration date.

The reason being we wanted to  postpone the travel.

Thanks

[pontevecchio]

They have 6 months to enter with the IV from the date of visa issuance.

[JoeF]

An immigrant visa is usually valid for 6 months. The validity should be printed on the visa.