What military power would ever pre-announce an attack to give the enemy time to work up a defense?

To partly answer your question in the title: The first recorded account is the Thebans, allies of Sparta. Against Athen's ally Plataea, they launched a surprise attack without a declaration of war. That started the Peloponnesian War.

Given that mobilising an army took a very considerably time and effort before professional armies were created, any declaration of war would be just a vain effort to mask a surprise attack with a notion of chivalry.

As to the modern idea of regulating war, which is probably a result of the Treaty of Westphalia that constituted the first kind of world order: It may or may not have applied to Japan. I'm not deep enough into the history of international law.

The question specific to Pearl Harbour had been answered by others: there was no declaration of war before the attack, and that is why it is called a "surprise" or "cowardly" and emphazised as such.

About other events where a country did notify an other about the war to come, largely before fighting actually occured, there is:

• Gulf War (second, 1991): from August 1990 to January 1991, UN forces were deploying but did not fight against Iraqi forces until January.
• 1948 war: Israel was threatened of war and actually invaded with not a lot of fights, because Arab countries did not know what they wanted to do actually. They started slowly and it gave some time to Hebraic defense forces to be organized.

You would issue a declaration of war to "legitimize" hostilities. Ideally, you trick the opposition into declaring a war they are ill prepared for... (Ems Despatch)

You would link that declaration of war to an ultimatum if there is hope that the opposition might yet step down from their position, and/or to further strengthen the impression that you really were given no other choice but the military option.

But there has been somewhat of a history of formal declarations of war being omitted in favor of achieving surprise (the kind which had become possible with the advent of highly mobile warfare):

• Germany on Poland
• Soviet Union on Poland
• Soviet Union on Finland
• Germany on Denmark and Norway
• United Kingdom on Iceland
• United Kingdom on Vichy France (Mers-el-Kébir)
• Germany on Yugoslavia
• United Kingdom on Iraq
• Operation Barbarossa
• Anglo-Soviet Invasion of Iran

...and half a dozen others listed elsewhere.

The interests of Japan and USA in the Pacific theater had been clashing for quite some while. The latest US embargo (25 July 1941) resulted in two options for Japan -- the military option (which would effectively necessitate neutralizing the US Pacific Fleet), or abandoning their empire. To this end, also see the Wikipedia article on the Hull note and the surrounding events.

The USA were definitely aware that hostilities were imminent. That the attack on Pearl Harbor happened without a formal declaration of war was convenient for the US narrative, and so was and is stressed whenever the subject comes up.

Declarations of war were normally made at the time via an ultimatum: "Unless you do something by date and time, then we shall be at war". This only says "we will be at war", it does not say anything about how the war will be fought. This was the form, for example of the British and French declarations of war on Germany in 1939.

The Japanese did not issue an ultimatum before attacking Pearl Harbor. The "14-part message" to the Japanese Embassy in Washington DC that the US decoded before the attack did not contain an ultimatum, although it did say that diplomatic relations were to be broken off. This was interpreted as meaning that attacks might take place, and warning was sent to US bases in the Pacific, but was not received at Pearl before that attack, owing to bad radio conditions.

It wasn't "cowardly or sneaky" of the Japanese to omit mentioning the date and time of their attack, it was "cowardly or sneaky" of the Japanese to start dropping bombs and shooting before they declared war.

At that time the rules of warfare required declaring war before starting to fight. A government was supposed to deliver an official announcement to the other government that there was a state of war between them, thus telling them that the hostile government forces might attack anywhere and anytime they considered desirable. And after delivering the message the country that declared war was free to begin attacking.

In this case the Japanese ambassador did not deliver the declaration of war in Washington DC until hours after the first bomb dropped and sometime after the government in Washington was informed of the attack on Pearl Harbor.

Article 1 of the Third Hague Convention in 1907 states:

The contracting Powers recognize that hostilities between themselves must not commence without previous and explicit warning, in the form either of a declaration of war, giving reasons, or of an ultimatum with conditional declaration of war.

https://ihl-databases.icrc.org/applic/ihl/ihl.nsf/ART/190-190002?OpenDocument1

Japan signed the Hague Convention 18 October 1907 and ratified it 13 December 1911.

The United States of America signed the Hague Convention 18 October 1907 and ratified it 27 November 1909.

https://ihl-databases.icrc.org/applic/ihl/ihl.nsf/States.xsp?xp_viewStates=XPages_NORMStatesParties&xp_treatySelected=1902

So Japan was legally bound to declare war before starting to fight the USA which was another contracting power of the Hague Convention.

Curiously, there is an law of war that can be interpreted as requiring a previous warning of a specific time and place of attack:

Article 25 of the Fourth Hague Convention in 1907 states:

The attack or bombardment, by whatever means, of towns, villages, dwellings, or buildings which are undefended is prohibited.

https://www.loc.gov/law/help/us-treaties/bevans/m-ust000001-0631.pdf3

Clearly "attack or bombardment, by whatever means," would include attacks or bombardment by airships and airplanes in 1907, since the first Zeppelin flight was in 1900 and the first airplane flight was in 1903.

The next article, Article 26, says:

The officer in command of an attacking force must, before commencing a bombardment, except in case of assault, do all in his power to warn the authorities.

https://www.loc.gov/law/help/us-treaties/bevans/m-ust000001-0631.pdf3

I interpret this to mean that it is forbidden to bombard, by whatever means as in the previous article, a town, village, dwelling or building, without warning the civilian authorities in the place, except when one's ground troops are actually assaulting the place.

If that is the correct interpretation, Article 26 was often violated in World War I, World war II, and other wars, where cities and towns were often bombarded by aircraft without warning given to the civilian authorities.