This card game was played by 3 women at a Sr Center and it took 3 hours. Eight decks of cards used to play this game.
Could it be Hand and Foot, a variant of Canasta? It uses multiple decks and has each player trying to build 7-of-a-kinds while emptying their two hands (the second being called the foot, hence the name). If they aren't playing cut-throat and instead just going for high scores, this game can theoretically go until every single card sans the 3s are melded.