The latest episode of Arrow explains the show's big time travel twist. Earlier in the season, Oliver's mission in the present and the adventures of his adult children in the flashforwards finally merged into one story when Mia (Katherine McNamara), Connor (Joseph David-Jones), and William (Ben Lewis) were mysteriously teleported to present-day Star City. It was there that they encountered Team Arrow for the first time.
In Arrow season 8, episode 6, titled "Reset", Oliver (Stephen Amell) and Laurel (Katie Cassidy) are placed in some sort of alternate reality where Quentin Lance (Paul Blackthorne) is still alive. Trapped in a time loop, the two try time and time again to save Quentin, but he dies every time. It doesn't end until they accept Quentin's death as something that has to happen. After waking up from the alternate reality, Oliver speaks to Lyla (Audrey Marie Anderson), who explains how this was a test set up by the Monitor (LaMonica Garrett) to make him understand that his death in the Crisis is inevitable.
Oliver asks Lyla why the Monitor chose to involve his children in his mission, and Lyla replies, "time is a gift". Apparently, the Monitor understood what he was asking Oliver to give up, so he allowed him a chance to connect with an adult Mia before making the ultimate sacrifice in the Crisis. This is the same reason why Laurel was given an opportunity to say goodbye to Quentin. It was all a reward from the Monitor.
That's essentially what it has seemed like for Team Arrow, particularly Oliver. Since their arrival, Oliver and Diggle (David Ramsey) have come to know their adult children, while others, like Rene (Rick Gonzalez), Laurel, and Dinah (Juliana Harkavy) have learned much about their future selves. Now that Team Arrow knows what happens in the future, they've decided to make sure things happen differently this time. In the meantime, both present and future versions of Team Arrow have been working together to help Oliver with his role in the impending Crisis. Mia and William even accompanied Oliver to Russia where they discovered surprising details about Oliver's dark past.
Now that Oliver understands the truth, it appears that he has finally accepted that he must trust the Monitor. In next week's episode, Oliver will take part in his final mission before the Crisis. Once that's over, "Crisis on Infinite Earths" will begin. Since the time travel twist has tied up a few loose ends and provided closure, Arrow is one step closer to ending Oliver's story.