Each country has its own regulation regarding the amount of advertising that can be transmitted

Italian law defines that:

the public service cannot exceed 12% of hourly advertising, any surplus, however not exceeding 2%, can be recovered in the next / previous hour

the free-to-air private broadcasters cannot exceed 18% of hourly advertising, any surplus, however not higher than 2%, can be recovered in the following / previous hour. However the total daily advertising cannot exceed 15%

Below is an analysis of the hourly advertising slots of an Italian private national broadcaster and the relative compensation for the previous and subsequent hours