Not starting a new thread for this but someone on a french forum seems to have leaked play times.
According to him, including the live action in every playthrough :
-His first play through took him 8h15 while exploring and searching for a maximum of objects (i don't know what he refers to)
-His second playthrough took him : 6h45-7h while making different choices. He spent a bit of time looking for other objects.
-Third playthrough : he rushed and it took him 6h. He made the choices so he'd have the storyline he liked the most.
Also according to him, QB is a game you have to play 2-3 times to be able to see everything. More is useless, but once is stupid. (his words)
Source : He deleted his post but it was quoted in the thread.