Translation:Early in the morning and late in the evening.
Here is one of those rare cases when the phrase in English is actually longer than in Polish
Indeed. Though, to be fair, you could as well say "Early morning and late evening" (Wczesny ranek i późny wieczór) in English to match the word count ;)
Actually I think it's better (easier?) to understand "wieczorem" as an adverb that just looks the same as Instrumental of 'wieczór'.
Or you can similarly use "rankiem" (from "ranek"), but "wcześnie rankiem" wouldn't work, you should also put it in Instrumental, "wczesnym rankiem".