My earliest predictions would be sometime this week. If not, then I'm almost certain there will be something next month. When they announce something, it's something that they are confident the up coming content they plan to release for the game will make it at a scheduled time.
They aren't an indie team who reveals something that may face whatever over time that may keep their goals from happening for god knows how long with or without clarification, as I've seen plenty of indie game teams that do that, they reveal and announce things as surprises with complete confidence when they are completely ready, as what any mainstream video game studio company like Frontier Developments themselves would do. Content exceptions can exist for anyone as cases of vaporware or schedule delays, but exceptions are exceptions.
In regards to DLCs, I think there will be at least one or two small DLCs like dinosaur packs, along with patches with general updates, bug fixes, and/or new free features albeit at a small scale. Bigger DLCs tend to be within a period of several months of development, considering how much work would be added within them along with huge updating patches with various bug fixes, general updates, and new free content simultaneously.