How long does preproduction last after a pitch? I would've thought they'd have to have at least the core design down
I have no idea, but for this case I estimate before the pitch they may have spent 3 to 6 months and once the pitch got greenlighted from 6 months to a year or a year and a half aprox.
It depends on the case, depends of a lot of things: in a AAA it can range from a few months to a couple years. It depends of the amount of things they have to research, evaluate if would work in the market or not, design, prototype and test. In a case like when EA makes the next FIFA and everything is pretty much the same than in the previous game is very short. It also depends if in the preproduction they want to make a vertical slice and how meaty, different to what they did previously and long it is what they have to test there in the vertical slice.
When they move to a new engine takes longer, when it's a new IP takes longer, when it's a new genre for them takes longer, when it's their fist AAA or open world game takes longer, when it's their first next gen game takes longer, when they have key mechanics pretty complex and different to what they had gets longer.
In this specific game, I think they'll move from UE4 they had in Days Gone to UE5 and that they'll use the main core mechanics from Days Gone but will add on top MP elements and maybe even GaaS stuff, and will have to design a brand new IP with its world, setting, artstyle, story and characters. Maybe also replace the hordes key selling point for another one like very dense cities and maybe some key new mechanic with let's say stealth. I assume that they also had to wait until UE5 released and spend some time doing tests with it. I bet they wanted to make a short vertical slice to test some new UE5 visual stuff, the new world setting, new main character design, and new look and feel, and one or two new main mechanic on top of Days Gone mechanics.
Probably it could have taken them a total of around a year, or a year and a half of preproduction. Having spent like 3 to 6 months from that before sending the pitch with a very small team of only like a dozen people working on it, and then aprox. from 6 months to a year after getting the greenlight with pretty much the whole studio working on the vertical slice. In other case it could have taken less time but they had to wait to UE5 release and also had the lockdowns in the early stages of the preproduction.