En dash–

The en dash is this line.

–

It’s longer than a hyphen but shorter than an em dash.

Forget about it.

Its formal use cases range from connecting a prefix like “pre” to a proper noun:

• Pre–World War II
• Pre–Industrial Revolution
• Post–Great Depression
• Non–European Union
• Mid–Victorian Era
• Anti–Wall Street movement
• Cross–Atlantic journey
  
  

And showing time frames:

• May–September
• 15th July–4th August
• 10am–2pm

I don't think you have to worry about all this. I’ve never used an en dash. There are clearer, less fussy, and kinder ways to say the same things:

• Before World War II
• Pre World War II
• Pre-World War II
  
  

That last one’s a hyphen. I included it because, if you must include a dash, the hyphen is a key on most keyboards, whereas an en dash and an em dash need a combination of keys to create them.

ctrl + shift + close one eye + shout the word LOGANBERRY 3 times = en dash

I would choose Pre World War II because it uses the least fuss to say the most.

There are better ways to display the time frames too:
 

• May to September
• 15th July to 4th August
• 10am to 2pm
  
  

They’re all equally as clear and easier for people who use screen readers.