How exactly do the Early Bird/Night Owl Town Ordinances work?

According to this site the key benefits of either the Early Bird/Night Owl town ordinance are:

• The villagers of the town change their schedule to fit the new time
• The villagers wake up and the shops open a varying number of hours earlier/later

But do they shift the opening hours or extend them to either 3 hours earlier/later?

E.g. if I choose the Night Owl ordinance, will the shops still open in the morning at the regular time? I cannot check right now because I'm not that far into the game and the information I find is kind of vague.

The Early Bird and Night Owl extend the hours, not shift them. So using the Early Bird ordinance will result in all shops opening 3-4 hours earlier (depends on the shop) and closing at the regular time. The night Owl ordinance will result in all shops open at regular time, and closing 3-4 hours later.