Oooh, totally missed the light sensor gimmick cartridge, love it!
Great job making that work! Are you planning on more light sensor related features?
The monsters turn into stone during the day, which is helpful because they will attack you, but also less helpful, because you need to use them to solve puzzles.
Some doors open and close depending on time of day.
The various kinds of fruit in the game, (You feed fruit to monsters in order to befriend them) are harvested in different ways, usually involving switching between day and night mode.