Where does a mouse go during the daytime?

Most definitely. 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. Things that can cause mice to leave their shelter would be disturbances towards their current shelter. If they feel threatened, or perhaps sense a danger in their vicinity. Sometimes they may be seeking out a second shelter area and are desperately in need to get away they will run out during the day time.

Hope that helps!