Work hours does not include Lunch breaks. Legislation specify 8 hours in a day or 48 hours in a week and this does not include Lunch Break I am not sure about Kerala Shops and Establishment Act. But to my knowledge legislation in India specify 8 hrs in a day and 48 hrs a week excluding Lunch break.
Scenario 1
If you work 5 days a week, then your work hours could be 9 hrs a day on all five days excluding lunch break
Scenario 2
If you work 5.5 days a week, then you can work 9 hours for six days excluding lunch break and just three hours on Saaturday. 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 Satuday as many legislation provide for lunch break after five hours and practically it is difficult to ask people to come for half an hour after 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 hrs a week. Including lunch hour it could be 9 hours.