The Rodent Guide
Usually, a mouse will only go out hunting for food during the evening; however, it will go out during the day if the mouse is particularly hungry.
I do not think you are going to like this reason! One common reason you have seen a mouse during the day is that you have a local infestation.
A mouse might venture out during the day because it has sensed a predator nearby and has beat a hasty retreat
Similar to food, mice need water to survive. If the mouse is thirsty, then it will venture out during the day to get some water.
If a local nest has been disturbed by a predator, by you, or by another human, then you will see mice during the day in that area.