Translation:Years, days, hours, how many?
an and année are more flexible than others and could more or less be used interchangeably.
Here's a quote from the link above: "However, note that an/année is far more flexible than the other pairs; for "last year" you can say l'an dernier or l'année dernière, "next year" can be l'an prochain or l'année prochaine, etc"
Found this, looks useful. http://french.about.com/od/vocabulary/a/an-annee-jour-journee-matin-matinee-soir-soiree.htm
It has nothing to do with short v. long, let alone masculine v. feminine, rather with the perception and standard usage. While an and année share the meaning of Durée conventionnelle voisine de la période de révolution de la Terre autour du Soleil, the latter is associated with a period 12 month long, starting at any moment of time, whereas an starts on January the 1st.
The above is a non-native's analysis
According to Larousse, "l'an" has to do with a 12-month duration, whereas "l'année" has to do with a "calendar <ou> civil year". So one might refer to "l'année 1789", for example. This also helps us understand why a person would say "J'ai 30 ans" instead of "J'ai 30 années" to express their age.
All your questions about l'an vs. l'année, le jour vs. la journée, le soir vs. la soirée, le matin vs. la matinée, are answered here: http://french.about.com/od/vocabulary/a/an-annee-jour-journee-matin-matinee-soir-soiree.htm It will require a thoughtful reading to master it but it is all there.
Shouldn't this sentence have a semicolon or an em-dash before "combien/how many?"
It would seem to make more sense in English, but I'm still not very familiar with French punctuation conventions, so I don't know if that works.
It is confusing to read because "combien/how many" is a separate clause that should be distinguished from the preceding series by something stronger than a comma.
Incidentally, this is also a line from a song called "Combien de temps encore" by Jean-Loup Dabadie. This guy seems also to be a member of the Académie française . Could also be coincidence.
You can easily imagine the context for this sentence, and if you do you'll see that the "combien" is not referring to the years, the days and the hours but to time itself, hence "how much".
Say you have an accident and you lose the sensitivity of your legs and the doctor says to you "It will take time for it to come back". Your response would be somewhat like this, I'm sure.