Whilst it hasn't (to my knowledge) been confirmed, the latest episode of Arrow had Ollie specifically ask Diggle to make sure the kids got back to 2040, so I think we can certainly assume that'll be where this show takes place. What I also found interesting is that Ollie also asked Diggle to ensure that Mia and William grew up together, rather than apart. If that's to then take place, would the Mia and William of the spinoff show have grown up together, or would they have been the duo that we've watched this season? Would they suddenly remember two timelines? Even though the show is supposed to be about Mia and the Canaries, I wouldn't be remotely surprised if Dinah is written out, or dare I say it, killed off shortly into the show. Despite it's namesake, this show is very much going to be about Mia. The Canaries, in addition to Diggle's kids are going to take a hard backup characters here. It isn't, it's just an easy spin to roll with characters they've already got, and have already invested in. Ollie's whole mission statement was to save his city, and if Mia and the Canaries are operating in 2040, then evidently Ollie will have failed in his initial mission, leaving his kids and the canaries to continue to clean the city up. Besides, it's kind of an insult to the Arrow legacy. Instead of ending Arrow on a high, they're going to pass the torch to Mia and let it run on. So much for the ultimate sacrifice.