The intention was for the Japanese embassy in Washington to convey the breaking off of diplomatic relations less than an hour before the attack was to take place.

Japanese military planing of the operations critically depended on the American military facilities to be unprepared and not be able to defend themselves.

It was for all intents and purposes, a surprise attack.

Maybe.

There was indeed a warning meant to be delivered 30 minutes before the attack that was not delivered until 20 minutes after the attack.

The official reason for the late delivery of the warning is a security rule that disallowed the embassy's American secretary to type up the document.

However, it is believed by some researches, such as former ambassador Takeo Iguchi, that the message delivery was deliberately delayed by elements within the Japanese military. He bases his theory on a declassified war diary which shows elements of the Japanese general staff were in disagreement with the Foriegn Ministry on how to proceed. He states that "The diary shows that the army and navy did not want to give any proper declaration of war, or indeed prior notice even of the termination of negotiations,"

He goes on to theorize that the final warning message was deliberately delayed by Tokyo, claiming that the message was purposely garbled when sent to the embassy.

Iguchi's claims are controversial, especially in Japan.

If you read the link provided in the link it's to the 14 Part Message which is supposedly a declaration of war. However, it actually contains no declaration of war. It's rather wishy washy. It pretty much only hints at cutting off negotiations with the USA. That in and of itself isn't a declaration of war but it seems that's the bit that people view as a declaration of war, but it contains no language saying that a state of war would exist between the USA and Japan, it gives no ultimatum with an expiration after which a state of war would exist, etc.

I know this is the third rail of askhistorian, but is there any knowledge or god forbid, 'speculation' on why the Japanese even bothered to send an official message prior to the attack?

It would be interesting to think about how the Attack would have played out if US forces in Hawaii would've received 30 minutes, an hour, or some other set amount of time to prepare for it. IIRC from my school days, the Carrier fleet was off to the West and South of the Islands, though I don't know if their planes would've been within intercept range or not. The Radar masses that were detected would've probably been looked upon far more suspiciously and AA defenses would've hopefully been brought to bear. I wonder how long it would've taken many of the ships berthed at Pearl to make way and head to Sea. I know at least 1 or 2 were running and attempting to exit the Harbor while the Attack was still going.