We are much faster now than we were before, I believe that a chapter will take 3 months from now on based on the speed we are going right now.
For example, the full chapter 3 is as big as a chapter and I'll be able to, hopefully, release it next month already. We started doing after Kain returned in February, so three months for a entire chapter-worth of content.
Also, keep in mind that each Era is self contained. I have these 20 games as a goal, to avoid reboots or "parallel universe" stories/if scenarios and the like. I only worry about the bronze age now. The rest will come when it will come.