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.
I can only tell you what happens in a mouse, but it's roughly analagous: 1  Day 1-2: A cell that makes antibodies a little bit specific (low affinity) activate and move to a lymphoid organ. 2  Day 2-4: Concentrate vaccine at lymphoid organs, and cells begin to proliferate, but still not that fast.