If one gets a 5 -year B2 tourist visa to the US (to attend son's graduation) but does not go to the US at the time, can he/she travel to the US at a later date without any problem? I've heard people say that one must visit the U.S within 6 months of issuance of B2 visa, but I couldn't find anything similar mentioned in an official source. I know that the visa holder must prove a valid reason for entering the US at the port of entry but my main concern here is whether the B2 visa holder can enter the US even though he/she did not do so within 6 months of visa issuance.