Episodic release is not all about "making money". For one, you bring more attention to the project. 5 releases mean more media attention than just 1. You are also correct that you get something faster than just waiting for the full thing, and it also serves us in fixing things as we go along. I can't tell you exactly how much time it'd take right now, but basically, all the way down to the last finished episode, minus possible a month or two because of rework based on feedback, releases, etc.
We are adapting the episodic model for our games. We believe it's a model that works for us, and allows us to put commercial products out there while sustaining the company to be able to do so. So, yes, Corridor 9 is planned to be a 4 episodes game at the moment.
Cez