A little midge sung a song around a person, who was sleeping in the bed at night.

> _How does the little busy me  
> **Improve each shady hour**  
> By setting on your nose or knee  
> As if upon a flower_

This is a short story from the novel "Little Old Mrs Pepperpot"

I couldn't understand the meaning "Improve each shady hour".
Does it mean "get light"? Could you teach me the meaning?