Adults usually fly at dusk, during the night, and at dawn, but they will also fly during the day. I photographed this one around noon here in Arkansas.
White-lined Sphinx Moth Facts
White-lined Sphinx moths with their large, plump bodies and relatively smaller wing surfaces must beat their wings very fast in order to stay aloft. Although they are constructed very differently from hummingbirds, White-lined Sphinx moths are able to hover hummingbird-like in mid-air as they sip flower nectar due to their similarly rapidly beating wings. (Source:Firefly Forest)