You are using terms in a loose and nontraditional way.

The argument isn't logical so much as it is valid. It isn't sound, based on the untrue premises, but it preserves the truth of the premises.

http://en.wikipedia.org/wiki/Soundness

Occam's razor provides a reasonable metric for burden of proof. Any position that requires Saturday to have a special property that affects light switches is obviously more complicated than the null hypothesis that light switches are agnostic with respect to the day of the week. The valid arguments in favor of a special Saturday are not terribly satisfiable (in a technical sense), and are thus unfavored.