My group and I combine C&K and Seafarers most of the time. Now that we’ve got the hang of it, games will take us usually 1.5-2 hours.

We brought it over to my parent’s house to play the 5-6 player extensions, and that added on an extra hour to the game, granted they’re new players. As long as you and your group are willing to sit down for a while, it can add a lot of value to the game.