"Are there languages/cultures where this isn't the case?" Well when it's not obvious in french you'd typically add "du matin" or "ce matin" to mean it was in t

"Are there languages/cultures where this isn't the case?" Well when it's not obvious in french you'd typically add "du matin" or "ce matin" to mean it was in the morning. But if you meet someone at 5pm you typically would just say : "Je me suis reveille a 8 heures". No need to say "8 heures du matin" or "8 heures ce matin" because it's pretty darn obvious. However you can add "du matin" / "ce matin" : it's certainly not a fault and many people do it. Now regarding the afternoon, you have the choice in french : either you use 12 or 24 hours. For 12 hours, it's the same as for the morning : 4 pm can be "4 heures de l'apres-midi" or "16 heures". 8 pm can be "8 heures du soir" or "20 heures". I typically use the 24 hours system because there's no ambiguity. Now I don't know the official rules and it's certainly often contextual. If someone asks you what time it is in a bar at night, it's pretty obvious when you answer "11 heures" that it's 11 pm but "23 heures" is good too. Same if you answer "2 heures", you then obviously mean 2 am, no need to say "2 heures du matin".