It depends. The earliest they could start working on a sequel as soon as they finish working on the first game or after it's released. Example: R&C 2 production began right after they finished R&C 1.
DLC production could begin at any time once it's planned i
s what I assume
Umm im only in my 5th week of my game designing class (i also learn alot about the gameing industry from that class) so ill give it my best shot. I think they have separate teams for working on DLC and working on the sequel so both ar being made at the same time untill they are done making DLC and that team starts hepling with sequel too.
Six months to a year for full production. However, they won't need a full team to do the DLC, so they could have 2/5 patching, 2/5 doing DLC, and 1/5 doing something else (writing for a sequel if it gets greenlit shortly after launch like it's going to, or something).
Yes turns out i know more **bleep** than i tought