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.
In cities, some mice may spend their entire lives inside buildings. In rural and suburban areas, may live in buildings, but is often found outdoors among shrubbery, weeds, foundations, crawl spaces, storage sheds, and in garages. Mice outside feed on insects and weeds seeds.