Yes, you're right. A realistic approach would be better. One hour ingame should last 60 real minutes. But if the day and night cycle is tied to the system clock of the computer, many people who work during the day could only see the night in Far Cry 3. This problem might be solved with a time skipping feature, in some games known as "sleep". The safe houses are perfect places for this feature, but other enterable buildings and caves might also be used.