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.
Mice are nocturnal, meaning they like to sleep during the day. This is why pet mice or house mice can be heard playing or foraging during the night. Most wild mice are timid toward humans and other animals, but they are very social with other mice.