Punctuality is the politeness of kings.
Meaning of the quote
Being on time shows that you respect others, just like how kings and queens are expected to be punctual and polite. This quote suggests that being punctual, or arriving when you say you will, is a way to demonstrate good manners and consideration for the people around you, even if you are in a position of power or authority.
About Louis XVIII
Louis XVIII was the King of France from 1814 to 1824, except for a brief interruption during the Hundred Days in 1815. He spent 23 years in exile before finally being restored to the French throne, and his reign was marked by the formation of the Quintuple Alliance and a military intervention in Spain.