en.wikipedia.org/wiki/Kornilov_affair

This clause conflates two separate events.

1. What happened on 1 (14) September 1917: the Provisional Government proclaimed Russia a republic. The Presidential Library of Russia's page on that decree says Russia was proclaimed a republic on 1 (14) September 1917 and then adds that the All-Russian Democratic Conference was convened on 12 (25) September, where a decision was taken to create the Predparlament (Pre-Parliament).

2. What happened later: the Provisional Council was not created on 14 September. In a U.S. State Department publication reproducing Kerensky's declaration of 25 September / 8 October 1917, the text still says that "a Provisional Council will be formed"—showing it had not yet been created even by that later date.

3. When it was actually formed and what it was: Encyclopaedia of Russia identifies the Provisional Council of the Russian Republic as a "consultative organ under the Provisional Government" and dates its formation to 20 September (3 October) 1917.

So the article's wording is incorrect in two ways: it says the 14 September proclamation created the Provisional Council, and it describes that body as a temporary parliament created at that moment. The evidence shows the republic was proclaimed on 14 September, but the Provisional Council was only proposed later, formally established in early October, and was a consultative/advisory body.