So I was wondering how long is this ?

It says an average session is about a few hours, assuming a few hours mean 3 hrs

And the fact that there are 31+ updates 

Does that mean it'll take 105 hrs to finish the whole thing?

nope.

i estimate the fisrt playthrough between 16-42 hours depending how capable you are, the hero build you are playing and if you skip certain content.

To unlock every cutscene you need at least two playthroughs (Bull Route  + Perfect Good  Ending). If you wanna learn more about the perfect good ending, use the search funtion and look for a thread with the name "good ending". Once inside look for "best good ending".  And don't ask further question about the war ending, because the thread + official guide already anwsered basicly every question.

So it would take (in total of everything in the game/novel) 64-168 hrs?