First, do you have any code you want to use, if so, please post it! Secondly, i wouldn't use a photo resistor do it inconsistencies such as clouds, shadows, birds:), etc...
Personally, i would use delay if that is all you need to do and you don't need to be able to move to actuator manually. I know someone will suggest using millis, but i would not use it for something that will need to run for more than 49 days because it will make the code more complex due to the fact that millis() will become to large and will need to be reset. Also, it would not be necessary for a code like this.