From the moment, I first get an idea for a story, I keep it in a stash with other ideas and then slam them together over time, so by the time I need to start working on the official outlines from beginning to end, I crank them out like a factory LOL.
It took me about two months to outline the whole 30+ chapter story I'm presently drawing. After revisions, it ended up being 50 comic chapters long because I had to slice a few outlines in half/in thirds and add/cut things out. I'm actually writing the finale scripts right now.
My second project was different, because it's about a business that profits off of holiday sales, so every outline called for episodic stories revolving the chosen holidays. It literally took me only four weeks to outline through 30+ chapters.
As for my 50+ and 60+ stories, it took about four months each and I'm letting those sit and cool off for a few years before I start officially working on them.
I know outlining is not for everyone, but what I love about it is that it allows me to control the flow of the plot, because when I go in cold turkey and jump into the chaos I just make a tedious mess of excess plot. This way, all I have to do is build scripts straight from the outlines and emotionally negotiate with my original decisions through the revision process.