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.
At a minimum, however, you should spend a few minutes in the morning, and a few minutes in the evening with each of your mice. These few minutes should be spent performing a health check. Mice can become deathly ill, very quickly; this is why a health check should be performed twice a day, every day.