You've got two agreements confused! But no matter, because this is still an applicable question.

Firstly, the agreement signed on the 11th of November 1918 was the Armistice of Compiègne. It was an official ceasefire between the two fighting sides(Germany vs. everyone else), and was conditional upon Germany fulfilling a set number of promises that included withdrawing their forces from certain territories.

Secondly, it was not signed at 11am, but at 5am! The men who signed it however, agreed for all fighting to cease at 11am, giving all participants six hours to communicate news of the armistice, and the orders associated, to their forces. This was important, because if the armistice was not followed completely, it was to be deemed void, and fighting would resume.

For that reason, it was vital that the time when the armistice began was clearly defined, and that there was enough time to communicate this widely.

The Treaty of Versailles was signed on 28 June 1919, and was the official peace treaty of WWI between Germany and everybody else. You might remember from high school history classes the Treaties of Saint-Germain(Austria), Neuilly(Bulgaria), Trianon(Hungary), and Sevres-Lausanne(Ottoman Empire). These were the other treaties signed between nations to officially declare peace after WWI.