Perhaps the authors thought that actual burglary would be more common at night, and that a proprietor during the daytime would be better positioned to shout "stop! thief!" and expect it to do anything, such that if we find you with a corpse in your house at night we have fewer grounds for suspicion (of you) than if we found it during the day. The logic seems pretty similar to the presumption that a woman raped in the countryside resisted, and is therefore merely damaged goods rather than an active participant in the sexual injury to her husband or father, as opposed to women raped in the city, who have an obligation to call for help.