In other words, a proper declaration of war that's not followed by an immediate surprise attack (I understand that the declaration was to occur on the same day as the attack at Pearl Harbour).
Also, how long did it take the Americans in Hawaii to realize that their attackers were Japanese, or did people know that any attack could only ever be Japanese?
I don't have it with me to cite sections from, but John Toland's The Rising Sun: The Decline and Fall of the Japanese Empire, 1936-1945 is the best I've seen on the subject. There was a lot more debate about the actual attack itself in that a lot of the leadership objected to taking six main carriers out of the pool of ships to support the operations that started at the same time to invade the Philippines and Dutch East Indies.
With regards to "Americans in Hawaii" the length of time varied, but maybe on the order of minutes. Sailors in the Pearl Harbor area new fairly instantly as the planes were flying low enough that the red meatball was visible. Many airfields were visited by strafing zeros, so once again the people around these areas would have handily seen the rising sun insignia, assuming they weren't too busy scrambling for cover.
I'm fairly certain that even those further away had a pretty good idea who was attacking though. It was a surprise that the Japanese had managed to attack, but aircraft carriers were very uncommon back then (and are still somewhat so, statistically) and no other Axis power had them.