Just Cause 2: main story about 15 hours; story with some extras about 22 hours; 100% completion about 53.4 hours. These are IGDB player-submitted averages from 7 submissions, not a deadline or a prediction of your pace.
Source: IGDB player submissions
Community playtime data is not available for Just Cause 2 yet.
Game Tales keeps what happened between you and a game in one Tale you can keep building.