Sure, in the rejected pilot version, Gary Seven was a time traveler, but in the version we know, he wasn't.
Really? I mean, do we know for sure that the Gary Seven in Assignment: Earth
hasn't been on time traveling adventures?
Assignment: Earth wrote:
SEVEN: Please identify yourselves.
KIRK: This is the United Spaceship Enterprise. I'm Captain Kirk, commanding.
SEVEN: (to the cat) Yes, I heard him, Isis. We're aboard a space vessel. From what planet?
SEVEN: That's impossible. In this time period, there weren't (notices Spock) Humans with a Vulcan? You're from the future, Captain. You're going to have to beam me down to Earth immediately.
KIRK: Phasers on stun.
SEVEN: Careful, Isis. All right. Captain Kirk. My name is Gary Seven. I am a human being from the twentieth century. I was on my way
KIRK: Humans of the twentieth century do not go beaming around the galaxy, Mister Seven.
SEVEN: I've been living on another planet far more advanced. I was beaming to Earth when you intercepted me.
KIRK: The location of that planet?
SEVEN: They wish their existence kept secret. Even in your time, it will remain unknown.
SCOTT: It's impossible to hide a whole planet.
SEVEN: Impossible for you, not for them. Captain Kirk, I am of this time period. You are not. You interfere with me with what I have to do there, and you'll change history. You'll destroy the Earth and probably yourselves, too.
SPOCK: If what he says is true, Captain, every second we delay him could be dangerous.
KIRK: And if he's lying?
SEVEN: This is the most critical period in Earth's history. The planet I'm from wants to help Earth survive.
KIRK: What if it turns out you're an invading alien from the future?
SPOCK: A most difficult decision, Captain.
With the certitude that Gary's aliens will remain unknown in Kirk's time, Gary is displaying knowledge of the future. Additionally, Gary speaks of "this time period" as if he has knowledge of other time periods. Together that sounds like Gary's aliens can time travel.
Perhaps Gary has even been to the future himself, or that is to say, to the future that he's trying to make sure that Earth makes it to.
And a little later.
SCOTT [on monitor]: Still unable to analyze it, sir. It was so powerful, it fused most of our recording circuits. Could have brought him back through great distances, could have brought him back through time. There's no way for us to know.
Scotty's remarks are consistent with the idea that Gary's beam could be used for time travel.
Accepting that Gary is from the 20th century time period, as he and the Beta Five say, there is still evidence in support of his aliens being able to time travel.
Some people even think "Assignment: Earth" was a deliberate copy of Doctor Who, but that's rubbish. It's unlikely that anyone in Hollywood at the time was familiar with DW, since it didn't begin showing in parts of the US until the '70s; and most of the similar elements -- the Earth-based setting, the sonic screwdriver -- were introduced to DW after they were conceived for A:E. (The sonic screwdriver made its screen debut just 13 days before "Assignment: Earth" aired, but as stated, the original A:E pilot was written over a year and a half earlier, and it did feature the servo and Gary's other familiar gadgets.)
For the record, when I mentioned Gary's "sonic screwdriver" upthread, I was teasing. I didn't think for a second that either ripped off the other.