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.
If you do see a mouse during the day, you have a real problem. They usually only come out at night, and only during daylight, if they are having trouble getting food. The daytime mice you see, are not the aggressive mice in the group, but the ones that have to wait for the big guys to eat first.