WARNING: The following article contains spoilers for the latest episode of Agents of S.H.I.E.L.D.,"Know Your Onions," which aired Wednesday on ABC.
At the end of Agents of S.H.I.E.L.D.'s sixth season, Simmons unveiled a new iteration of the Zephyr with the ability to travel through time. With it, Coulson and his team were able to follow the Chronicoms to 1931 New York. There, the evil synthetic aliens planned on erasing S.H.I.E.L.D. from history, as it was the only organization preventing them from taking over the world.
Over the years, Agents of S.H.I.E.L.D. has often featured connections to the Marvel Cinematic Universe films. Sometimes, this connection was through a direct storyline, while in other instances, it was more of a thematic approach. The latter is the case with the television series' seventh season. In 2019's Avengers: Endgame, Earth's Mightiest Heroes traveled back in time to collect the Infinity Stones. And while the Agents of S.H.I.E.L.D. aren't directly involved in this mission, they too have their own adventure through the time stream.
But while the Avengers and Coulson's team are both traveling through time, they each have access to two very different time machines.
In Avengers: Endgame, the technology behind time travel revolved around Hank Pym's Pym Particles. After being stuck in the Quantum Realm for five hours -- which equated to five years on Earth -- Scott Lang theorized that time travel could be possible thanks to the subatomic reality. With this knowledge, Tony Stark was then able to create a time GPS, which allowed the Avengers to select their destination, both in time and space. He then designed a special launch pad which allowed them to access the Quantum Realm. With this technology, the heroes were able to reach the time periods of several movies, and operate for as long as they needed.
When things didn't go according to plan, Stark and Steve Rogers even went further back in time. All they needed to make sure they were able to come back were more Pym Particles, to once again enter the Quantum Realm.
In Agents of S.H.I.E.L.D., the time-travel technology is very different. In fact, in the Season 6 finale, Simmons briefly explains that the Zephyr has the ability to access specific windows in time, existing tides that they can follow. The Chronicoms reached 1931 New York through one of these windows, and the S.H.I.E.L.D. agents followed them. Now, in the latest episode, "Know Your Onions," we learn even more about the series' take on time travel. In truth, these windows through time are only open for an unspecified amount time -- it could be minutes, hours or days.
Once the window is about to close, the Zephyr begins a countdown, and the team has to get ready for a jump that will lead them to the next open window. Therefore, the team are only passengers to the Zephyr; they have no say in where or when they are going next, and they have no idea how much time it will last.
In Endgame, the Avengers were able to pinpoint their exact location, which allowed them to reach destinations they were familiar with. However, that's not the case for the S.H.I.E.L.D. agents. They have no idea what will be waiting for them on the other side of their next jump, which means they have to be ready for anything.
Agents of S.H.I.E.L.D.'s final season airs Wednesdays at 10 pm ET/PT on ABC. The series stars Ming-Na Wen, Chloe Bennet, Henry Simmons, Iain De Caestecker, Natalia Cordova-Buckley, Elizabeth Henstridge and Clark Gregg.