We are honestly not sure how long it is and we try not to think about it. Sure, we want to have a game that lasts a while, but our main concerns is for the experience to unfold in a certain way and to make sure that what is in there is as good, meaningful and varied as possible. To have a certain game length as a goal goes against our design philosophy.
I understand you all are interested in knowing the game length though
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Once we start doing tests of the full game we will probably be able to get some average completion time that we can share!