Hi Jean-Marc,
It seems our operation hours app was not updated on the app store yet. That is why you did not see the new features. We apologize for the inconvenience caused.
We have updated the app version in our apps page. I have also helped you update your hours app. It should be displaying fine now(http://take.ms/DW7k7).
You can configure the 12/24hr format in the page category custom fields page(http://screencast.com/t/Lyn0b9ZjGe).
Hope this helps.