Well, the first act is already on youtube
https://www.youtube.com/watch?v=UDYHKC_CJNI
and it last an hour and a half (tv show included). Still, we have to consider that act 1 part 1 is missing for plot reasons, so we have to add that. Part 2 and part 3 are each 30 min long, so if we assume the same for part 1, we can add other 30 min.
So first act + tv show episode could be 2 hours long.
Of course we have to consider that it all depends on how people play, and how much attention a player give on collectibles and reading stuff.