Grand jury is so named because traditionally it has greater number of jurors than trial jury, called a petit jury (from the French word petit meaning small).
Although mice tend to come out in the night when most of the occupants of the house are asleep or immobile. This allows them to stealthily infiltrate any of your food bags, crumbs etc. During the day time, mice will normally not come out, but if opportunities exist then they surely can.
That includes vampires, owls that like to hunt by moonlight, and that roommate who stays up playing video games until the wee hours of the morning. You've probably heard of nocturnal animals, like bats and fireflies, who sleep during the day and come out to play when the sun goes down.