I've heard that expression to describe the Spanish Empire, TIL that it's also used to talk about the British one.

From Spanish Wikipedia: El imperio donde nunca se pone el sol - Wikipedia, la enciclopedia libre

The expression The empire where the sun never sets has been used in different contexts to define a certain type of global empire, so extensive that there is always at least a part of its territory where it is daytime. It was originally used by the Spanish Empire, mainly between the 16th and 17th centuries. In more recent times it has been used for the British Empire, mainly in the 19th and 20th centuries.