I have both of them in front of me and they are both rather long. Well 1900 twice as long as Indochine at 5 hours, but would welcome DUer comments.
1900 (1976)
http://www.imdb.com/title/tt0074084/Set in Italy, the film follows the lives and interactions of two boys/men, one born a bastard of peasant stock (Depardieu), the other born to a land owner (de Niro). The drama spans from 1900 to about 1945, and focuses mainly on the rise of Fascism and the peasants' eventual reaction by supporting Communism, and how these events shape the destinies of the two main characters.
Indochine (1992)
http://www.imdb.com/title/tt0104507/Indochina during the 30's. One of the largest rubber-tree plantations is owned by the French colonist Eliane, a proud but imprudent woman. She lives with her father and her native adoptive daughter Camille. At an auction Eliane gets to know the young officer Jean-Baptiste; after a short affair she refuses to see him again. But in the meantime Camille falls deeply in love with the young man, so Eliane takes the necessary steps to cause a transposition of Jean-Baptiste onto a far island. Though Camille gets married to another guy she goes on a long journey throughout the country in order to find the man she loves.