Far Cry 3: main story about 16 hours; story with some extras about 21.6 hours; 100% completion about 34.5 hours. These are IGDB player-submitted averages from 13 submissions, not a deadline or a prediction of your pace.
Source: IGDB player submissions
Community playtime data is not available for Far Cry 3 yet.
Game Tales keeps what happened between you and a game in one Tale you can keep building.