It appears it can be submitted 72 hours in advance, and the form does not ask for any details of your flight. So it shouldn't really affect check-in at all. Haven't seen anything to indicate that airlines will be required to check for this.

Between passenger manifest info from the airlines, and the info submitted when applying for a visa, almost everything they ask for in this form should already be available to the immigration authorities. Perhaps the only missing piece is the declaration of "which countries have you visited in the last X days". Also, conceivably your local address could be different from what you had proposed in your visa application. Guess they want these things on file, for whatever reason.