Alabama is home to gray squirrels, fox squirrels, and southern flying squirrels, so “squirrel activity” does not describe just one animal or routine. Gray squirrels are active during the day, while southern flying squirrels are nocturnal; nighttime movement should not be dismissed simply because a gray squirrel was seen outside earlier.
Gray squirrels use tree cavities as well as leaf-and-twig nests, and that cavity-nesting behavior can bring them into attics and other sheltered parts of buildings. The useful question is not whether squirrels live in the neighborhood, but whether a particular opening gives them access to your home.
Family status also matters: Alabama Extension describes gray squirrel litters usually arriving in late February to early March and again in July to August. Its attic guidance warns that excluding a parent while dependent young remain inside can leave those young trapped; the calendar is a reason to investigate, not a substitute for checking the nest.