Question: How many hours before the United States did Great Britain declare war on Japan?
About the article "Attack on Pearl Harbor", section "Aftermath".

Candidate passages:
Joint Army and Navy Basic War Plan Red was a war plan created by the United States Army and Navy in the late 1920s and early 1930s to estimate the requirements for a hypothetical war with Great Britain (the "Red" forces).
War Plan Red discussed the potential for fighting a war with Britain and its Empire and outlined those steps necessary to defend the Atlantic coast against any attempted mainland invasion of the United States.
It further discussed fighting a two-front war with both Japan and Britain simultaneously (as envisioned in War Plan Red-Orange).
War Plan Red was not operationalized and did not have presidential or Congressional approval.
In the U.S. only the Congress can declare war, and it made no war plans.
President Herbert Hoover was known as a pacifist.
War Plan Red was developed by the United States Army following the 1927 Geneva Naval Conference and approved in May 1930 by the Secretary of War and the Secretary of Navy and updated in 1934–35.
In 1939 on the outbreak of World War II and Britain's war against Nazi Germany, a decision was taken that no further planning was required but that the plan be retained.
War Plan Red was not declassified until 1974.
The war plan outlined those actions that would be necessary to initiate war between Britain and the United States.
The plan suggested that the British would initially have the upper hand by virtue of the strength of the Royal Navy.
The plan further assumed that Britain would probably use its Dominion in Canada as a springboard from which to initiate a retaliatory invasion of the United States.
The assumption was taken that at first Britain would fight a defensive battle against invading American forces, but that the US would eventually defeat the British by blockading the United Kingdom and economically isolating it. 
The attack on the harbor took place before any formal declaration of war was made by Japan, but this was not the intent of the Japanese high command.
It was originally stipulated that the attack should not commence until thirty minutes after Japan had informed the United States that it was withdrawing from further peace negotiations.
It was the intent of the Japanese to uphold the conventions of war while still achieving surprise, but the attack began before the notice could be delivered.
Tokyo transmitted the 5,000-word notification (commonly called the "14-Part Message") in two blocks to the Japanese Embassy in Washington.
However, transcription took too long for the ambassador to deliver it in time.
Even so, the notification was worded so that it actually neither declared war nor severed diplomatic relations.
The UK declared war on Japan nine hours before the US did, partially due to Japanese attacks on Malaya, Singapore and Hong Kong, and partially due to Winston Churchill's promise to declare war "within the hour" of a Japanese attack on the United States. 
Hoover visited 10 European countries in March 1938, the month of Nazi Germany's "Anschluss" of Austria, and stated "I do not believe a widespread war is at all probable in the near future.
There is a general realization everywhere ... that civilization as we know it cannot survive another great war.
"Like many, he initially believed that the European Allies would be able to contain Germany, and that Imperial Japan would not attack American interests in the Pacific.
Unlike Roosevelt's administration, Hoover was a vocal supporter of providing relief to countries in Nazi-occupied Europe.
He was instrumental in creating the Commission for Polish Relief and Finnish Relief Fund.
When the Germans overran France and then had Britain held in a stalemate, many Americans saw Britain as on the verge of collapse.
Nonetheless, Hoover declared that it would be folly for the United States to declare war on Germany and to rush to save the United Kingdom.
Rather, he held, it was far wiser for this nation to devote itself to building up its own defenses, and to wash its hands of the mess in Europe.
He called for a "Fortress America" concept, in which the United States, protected on the East and on the West by vast oceans patrolled by its Navy and its Air Corps (the USAAF), could adequately repel any attack on the Americas.
During a radio broadcast on June 29, 1941, one week after the Nazi invasion of the Soviet Union, Hoover disparaged any "tacit alliance" between the U.S. and the USSR by saying:When the United States entered the war following the December 7, 1941, Japanese attack on Pearl Harbor, Hoover swept aside all feelings of neutrality and called for total victory.
He offered himself to the government in any capacity necessary, but the Roosevelt Administration did not call upon him to serve. 
On December 7, 1941, the Empire of Japan launched an attack on Pearl Harbor, Hawaii, beginning a war between Japan and the United States.
According to the terms of the Anti-Comintern Pact, Germany was obliged to come to the aid of Japan if a third country attacked Japan, but not if Japan attacked a third country.
Nevertheless, the German government chose to declare war on the United States, partially in response to previous acts of Anglo-American cooperation such as the Destroyers for Bases Agreement, Lend-Lease, the Atlantic Charter, the hand over of military control of Iceland from the United Kingdom to the United States, the extension of the Pan-American Security Zone, etc.
The German declaration of war came as a great relief to British Prime Minister Winston Churchill, who feared the possibility of two parallel disconnected wars (UK and Soviet Union versus Germany in Europe, US versus Japan in the Pacific).
With Nazi Germany's declaration against the United States in force, American assistance for Britain in both theaters of war as a full ally was assured. 
After reluctantly accepting the Harris Treaty, Japan quickly signed similar treaties, called the Ansei Treaties, with Russia, France, Great Britain, and the Netherlands.
This process was hastened by the outcome of the Arrow War in 1858 in which the Chinese were once again soundly defeated by the British and the French.
Harris also suggested that Japan sign "honorable treaties" before the allied Anglo-French fleet would sail to Japan and coerce the signing of "unequal treaties."
However, the content of those treaties did not differ in their most essential points from the Tientsin Treaty between Great Britain and China in 1858; one of the most prominent of the unequal treaties in the history of Eastern-Western foreign relations.