It could be also cause administrative laws regulating each country/municipality. For ex., in my former country, there is a law forbidding merchants to maintain their shops opened along more than 7 to 8 hours per day, unless a special agreement with the Major House is signed. So standard merchants chose the standard timing that's to midday and 3 to 7 PM. Out of bakeries: they are allowed by the same law to open at 7 AM.