The concept of "normal business hours" doesn't exist in France. I'm talking about the usual 9am to 5pm time period in the United States when you can safely go just about anywhere (banks, the post office, stores) and expect that they will be open. In France, each business/organization/government office chooses it's own set of operating hours. Some are closed Monday mornings, and some are closed Friday afternoons. Many are closed everyday for lunch, but you can't even use that as a general guide because each place has a different lunch schedule. Forget about weekends; almost everything is closed on Sunday, and Saturday is a wild card. The purpose of all this time confusion is simple: to make foreigners feel like bumbling idiots.
I learned the hard way that even separate offices within singular organizations don't always have the same hours. Numerous trips to the Sciences Po campus have been cut short by the discovery of an unexpected closure. First, it was the student ID card office. I foolishly made the rookie mistake of trying to get something done at 1pm. They were at lunch. Then there was the carte de séjour office, which helps students acquire the documentation they need to be in the country legally. They are only open Monday mornings and Thursday afternoons. The biggest disappointment was the language department. I was so excited to sign up for a French class, but when I got there, the office was closed. The worst part was realizing that there were actually people working behind that big door. I could hear them! But the office doesn't take visitors on Monday mornings. I felt like a bumbling idiot.
The only comfort in all of this is the knowledge that you're not alone. Nearly all foreign visitors to France can tell you about their frustration with schedules. Just yesterday a dear friend of mine who is currently in Paris doing research for his thesis told me about his attempt to visit the Bibliothèque Nationale de France early in the morning. He got up, got ready, and made the trip to the library only to discover that on Mondays, they don't open until 2:30pm. That night, we commiserated together over dinner. Thankfully, there are no inconveniences in France that can't be made better by good company, good food, and a big glass of wine.