Work hours do not include lunch breaks. Legislation specifies 8 hours in a day or 48 hours in a week, and this does not include lunch breaks. I am not sure about the Kerala Shops and Establishment Act, but to my knowledge, legislation in India specifies 8 hours in a day and 48 hours a week excluding lunch breaks.
Scenario 1
If you work 5 days a week, then your work hours could be 9 hours a day on all five days excluding lunch breaks.
Scenario 2
If you work 5.5 days a week, then you can work 9 hours for six days excluding lunch breaks and just three hours on Saturday. Alternatively, you can work 8.5 hours for five days (42.5 hours for five days) and five hours on Saturday, which will make the total 47.5 hours for the week. I am suggesting 5 hours for Saturday as many legislations provide for a lunch break after five hours, and practically it is difficult to ask people to come for half an hour after a lunch break.
Scenario 3
If you work 6 days, then you can never declare 9 hours a day. In this situation, you are advised to restrict 8 hours a day, which will make it 48 hours a week. Including the lunch hour, it could be 9 hours.