Italy backing Poland and exposing Germany's Austrian border

What happens if Mussolini backs Poland because Hitler starts the war before the agreed date?

Germany must worry about an Italian attack through Austria, Britain and France gain an unexpected partner, and Soviet calculations about Poland become more uncertain.

The scenario assumes Mussolini reacts to Hitler starting the war earlier than promised by backing Poland. Britain and France would welcome the change, while the Soviet decision about invading Poland becomes less straightforward. The immediate military pressure would fall on Germany's Austrian border, where few German troops are assumed to be available. Italy's lack of a direct land connection to Poland therefore does not prevent it from threatening Germany. Italian naval strength relative to Germany also counts in its favour.