Updated link for jour versus journée: http://french.about.com/od/vocabulary/a/an-annee-jour-journee-matin-matinee-soir-soiree.htm
This link suggests that, although the two terms are often used as if they were synonyms, a fine distinction can be made if required whereby "pendant" means at some time(s) during the specified period, whereas "durant" means for the entire period. http://languedepoche.cegepoutaouais.qc.ca/index.php/particularites-de-la-langue/p/177-durant-ou-pendant However this Duolingo translation clearly does not make this fine distinction, and WordReference allows both meanings for "durant" and "pendant"
http://www.wordreference.com/fren/durant http://www.wordreference.com/fren/pendant. So I went to Larousse where they say that, although the two words can often be used interchangeably, there is the fine distinction that can be made as suggested above i.e. use "durant" where you want to stress that something continues for the entire period, and use "pendant"where you want to stress that something occurs at some point(s ) during the period http://www.larousse.fr/dictionnaires/francais/durant/27036/difficulte I think we could therefore use either word for most purposes without being actually wrong, but could use the distinctions of register and usage explained in the Larousse link when a greater precision of expression was required.