You might get it done in 6 months, but there is something magical in game and in life when you can do things without the pressure of the clock. Throw the timer away and things change.
The question I have is why does it matter? If you are not finished with classic and DOF is released 4-6 months later , what changes for you ?
There is no one forcing you to not do content or be a completionist ? The argument for having content released every 4 or 6 months is about retention , the reality is if a large portion of the population finishes the content and have another 2 or 3 months of little or nothing to do but raid the server will take a huge population hit.
That means less people logging on , less people willing to join in what is perceived as a dead or dying server and less people in general willing to help you in whatever goal you are working on.
I just see overall extended time periods of waiting as the death of guilds even more for smaller guilds and the server in general .