Hegel used "Minerva's owl does not take off until dusk" as a metaphor for philosophy. He regarded philosophy as a reflective activity and a rational thought. If human "thoughts" and "knowledge" are compared to birds soaring in the blue sky with the rising sun, the owl that naturally takes off at dusk refers to "reflection."
There is another explanation for this sentence: In Hegel's view, philosophy cannot exceed its time. The emergence of a certain philosophy always lags behind the times, and therefore cannot teach the world any or guidance. He believed that philosophy always appeared after an era had ended, so he said it would only take off at dusk.