I've had some free time (and can't sleep), so I have what I think to be the "how" and "why" for Bryan Fuller and Alex Kurtzman settling on "when" DSC took place. This is me putting the pieces together in a way that I think makes the most sense. DSC was never intended to stay in the 23rd Century. The plan was for DSC to start off in the TOS Era, go to the TNG Era, and then go to The Future. Pulling a quote from Trekmovie.com relaying an article from Entertainment Weekly. Bryan Fuller’s Original Pitch For ‘Star Trek: Discovery’ Included Going Beyond TNG Era – TrekMovie.com So, originally, Bryan Fuller didn't even want to stick with the same crew from season-to-season, but CBS wanted him to stick with one crew. I don't know when the idea to create Picard happened, but we didn't hear anything about it until mid-2018 and they must've had the idea going on for a little bit, trying to work it out with Patrick Stewart, so the idea for PIC must've been floating around during DSC's first season. Though I think, based on the design of the Klingons, they didn't decide they wanted to do PIC until after they'd already gone through with redesigning the Klingons. Before production of DSC began, if they already knew they were going to eventually make PIC, I don't think Alex Kurtzman would've let Bryan Fuller redesign the Klingons. Because Alex Kurtzman wouldn't have wanted to have to deal with "Then what would Worf look like?" So, in turn, the idea to do multiple Star Trek series must've come a little bit later on, not right away. I'm going to assume that once Alex Kurtzman wanted to make PIC, the idea for DSC going into the TNG Era was dropped. They'd want to save re-introducing the TNG Era for PIC. So instead of going from the TOS Era to the TNG Era to The Future, they streamlined their idea to DSC just going straight from the TOS Era to The Future. All that leads me to believe that DSC was never intended to stay a prequel. Not even from Day One. "So why even go to the TOS Era at all?" The Kelvin Films were hot at the time, and they probably wanted to distance themselves from anything associated with the Berman Era, at least to start off with. Nemesis bombing and Enterprise getting cancelled early cast a long shadow. That ruled out the 22nd and 24th Centuries, leaving them with starting off in the 23rd Century before heading off to The Future. Then they could work TOS stuff in, which the Kelvin Films made popular again. Bryan Fuller wanting to tell a story based on something referenced in TOS fits in with all of that. It went with what they wanted to do anyway. So DSC was always going to start in the TOS Era and it was always going to go into The Future. It was just a matter of hammering out the specifics. That's why they had time crystals in Season 1 and the fake-out when Discovery left the Mirror Universe and ended up in the future... except it was only nine months in the future. It was a tease before they did it for real. And "Calypso" was them testing the waters for what they could do. Speculation Only: I think it's also why Discovery's sets don't look TOS-Like or Updated-TOS-Like. It's still television. They still have a pattern budget. They built the sets to be used across the entire series. Once they built them, they wanted to stick with them. They didn't want to have to build a whole new bunch of ship sets every season. So they went with something that wouldn't have such a TOS-y look once they weren't in that era anymore. I think that might've played a hand in them designing Discovery to look the way it did, inside and out. The Enterprise in DSC (and later SNW) looks the way it does because they weren't going to take the Enterprise out of the 23rd Century, so they went with "Updated TOS" for the Discoprise instead of "Updated Trek in General" like they did for the Discovery itself. Even here, though, they tried to split the difference. The Discovery was based off a design from the abandoned 1970s Star Trek movie, Planet of the Titans. So they could have their cake and eat it too, and say technically the original design was meant for a 23rd Century ship. It would've been a TOS Movie Era ship, which would make a TOS Movie Era design in the TOS Era be like the equivalent of a Concept Car. Fitting for an experimental ship with an experimental Spore Drive. In-universe, if it all worked out, Starfleet could've called it "The Starship of Tomorrow!" A direction they could've gone in. But of course, one way or another, the writers were going to make sure something would happen so it wouldn't be. This is how I see what their thinking must've been for the series and why they made the decisions they did. Whether those decisions were the right ones to make or the wrong ones to make can be debated forever. I'll be interested to see how much of this -- or if any of it -- actually turns out to be the case, once the Non-Disclosure Agreements expire and they can start talking these things openly.