At the beginning of each upkeep, if no spells were cast last turn, transform Hinterland Logger.
For more information on double-faced cards, see the Shadows over Innistrad mechanics article (http://magic.wizards.com/en/articles/archive/feature/shadows-over-innistrad-mechanics).
The abilities that transform a Werewolf back and forth look at the entire previous turn, even if the Werewolf with that ability wasn’t on the battlefield for some or all of that turn.
To trigger the Werewolf’s back face’s transform ability, a single player must have cast two or more spells during the previous turn. If multiple players each cast just one spell during the previous turn, the ability won’t trigger.