This is an excellent question! According to Birds of North America Online:
...On Baffin Island, Snowy Owls hunt in all weather and at all hours during the continuous summer light, although they are seemingly less active about noon and midnight (Watson 1957). On Greenland, they hunt mostly in early morning and late afternoon (Manniche 1910). More observations on foraging times are needed for both breeding and nonbreeding periods. Not known if these owls hunt at night, or even by moonlight, during winter darkness.... Thus any observations of hunting at any hour by this bird will add to the body of knowledge. Ed Furlong Evergreen, CO
