A reviewer took 15 hours to beat the main story once but he said he just did that mostly. So make it 11 hours long for the main quest. But honestly I don't think the main quest is the point of Cp77. As an RPG game wanna-be I suppose you gonna have to see the entire "main quest" as the whole package including every side quest since it's gonna impact your character, future outcomes and the experience in general. Saying CP77 has a main story and side quests isn't completely right in my humble opinion, and this is good since too many games make a straight out distinction between main and sides and you lose the immersion (and it becomes gamey).