Hello Emir,
Happy you asked, this is one of the questions that I love to answer personally.
Overall it can differ.
Lets start with the Writing side, that takes a while from first word written to completion. Its hard to really put down a time as DD, the creator, is still writing the story as we go on. Once he has written a Chapter that goes on ice until the Script Proof readers, Arglin and I, start working on perfecting the English in those chapters. that can take from a few days up to two weeks, coming down to the chapter length.
The Art, Music, Game programming etc. does take most of the time. I cannot speak for our talented Artists working on this stuff but the pieces do take a while, up to about a month generally to full completion. That can be made longer do to Real life stuff getting in the way or simply inspiration blocks. Which currently prolong the work on Chapter 4 before release do to the former currently creating some troubles.
I Can't obviously share much more than this, but I hope this could give you some perspective on the matter. We try our best to get these Chapters out with a good mix of Quality and Speed, in which case we generally prefer making sure the former is taken care of, with the later being rather unimportant.