Question: When did we begin to stand for the national anthem?
Disambiguated questions and answers: question: When did the law state that stand at attention during the national anthem?
When did the law state that men and women should stand at attention and face the direction of the music?
When did the law state that men and women needed to stand with their hands over their hearts?
answer: June 22, 1942
December 23, 1942
July 7, 1976
Natural Questions answer: June 22 , 1942 (from the Wikipedia article "The Star-Spangled Banner")