I know there has been some discussion on en dashes and spaces before, but I wonder if anyone knows an authority that supports what I have always considered good practice. I don't think it's my idea, but something I was taught years ago.
I believe that the range en dash should have no space around it if it joins the same units, so:
but should have spaces around if the range is being expressed by different units, so:
July 5 – August 6
4 July 1965 – 7 January 1966
This approach seems particularly better in the second case, because "4 July 1965–7 January 1966" results in a moment of confusion as the reader perceives the range as "1965–7", but even the first case "July 5–August 7" creates an unnaturally strong visual unit between the 5 and August.
I know the Chicago disagrees with me, but I think the Chicago is wrong.