То есть, как я понял, главное, чтобы физически было два диска, а продолжительность не важна.
Интересных фактов из Вики по теме:
The first double album was recordings from the Carnegie Hall Concert headlined by Benny Goodman, released in 1950 on Columbia Records, that label having introduced the LP two years earlier.
The first studio double album was French singer-songwriter Léo Ferré’s Verlaine et Rimbaud, released in December 1964 on Barclay Records.
The first rock double album was Bob Dylan’s Blonde on Blonde released on May 16, 1966. It was soon followed by Frank Zappa & the Mothers Of Invention’s debut record, Freak Out!, released on June 27, 1966.
The best-selling double album of all time is Michael Jackson’s HIStory: Past, Present and Future, Book I with over 33 million copies (66 million units) sold worldwide. The second best-selling double album and best-selling concept double album ever is Pink Floyd’s The Wall with over 30 million copies (60 million units) worldwide. Other best-selling double albums are The Beatles’ White Album, The Rolling Stones’ Exile on Main St., Billy Joel’s Greatest Hits I & II, Bob Dylan’s Blonde on Blonde, and The Smashing Pumpkins’ Mellon Collie and the Infinite Sadness.
Заппа конечно молодец