Nitpick: Why would a Romulan War Bird be orbiting around the space station? The gravitational pull of a space station is minimal so the Romulan War Bird should be stationary relative to the space station.
Goof: O'Brien is wearing an Ensign pip in this episode instead of the Chief Petty Officer insignia.
Goof: When O'Brien time-shifts for the second time and sees the fight at Quark's, he sees his future self being beaten up by a Klingon and thrown against the bar. When future O'Brien gets back up, and is again grabbed by the Klingon, we can see that his comm badge is missing. But when future O'Brien gets up after our O'Brien stops the Klingon, the comm badge is back.
It should be common knowledge in Starfleet that Romulan Warbirds use quantum singularities in powering their warp cores, as evidenced in The Next Generation episode, "Timescape". So why does it take so long for them to identify one so obviously noticeable, being in an elliptical orbit around DS9?
Goof: When O'Brien gets shot by the hidden weapon, you can tell the falling body is a stunt double with a bad wig.
future O' Brien: You look pretty bad.
O' Brien: Yeah, it's the radiation
future O' Brien: Well, if you feel bad, and you're my past self. Shouldn't I feel bad, too?
Both: I hate temporal Mechanics.
(talking about O'Brien experiences)
O'Brien: He was complaining about some Klingons - he said they'd damaged two of his holosuites.
Bashir: Well... you do have one problem: If all you can hallucinate about is Quark's maintenance problems, I'd say you have a sadly deficient fantasy life.
O'Brien: Trust me, Quark. Darts and bars go together like bacon and eggs.
Quark: At least people order bacon and eggs.
Sisko: The Romulans generally prefer to sit back and pull the strings from a distance if they can.
Kira: Well, this is one puppet who doesn't like her strings pulled.
O'Brien: I feel like someone just walked over my grave. I mean, I've had a lot of brushes with death in my career. But there was something about watching myself being killed... feeling my neck for a pulse that wasn't there...
Bashir: It could've been worse. It could've been me.
Kira: That's it! You can rip the cloaking device out of the Defiant right now! Those are all the questions I'm going to answer. And I suggest you avoid asking Odo those questions, or you just might find yourselves on the other side of that bulkhead floating home!
Quark: How is Deep Space Nine's most famous fortuneteller?
O'Brien: Quark, we go through this every time the Klingons come aboard the station. Why don't you just keep them out of the holosuites?
Quark: Have you ever said no to a Klingon? Besides, now they're paying me double.
Bashir: It's all right, Chief. You're okay.
O'Brien: No, I'm not. You need to run a basilar arterial scan.
O'Brien: Because if you don't, I'm going to die in less than five hours.
Bashir: Who told you that?
O'Brien: You did... in the future.
Bashir: Oh. Well, who am I to argue with me?
Sisko: Just be careful.
Odo: Commander, there's no careful way to question a Klingon.
Sisko: You really think Quark had something to do with this?
Odo: I always investigate Quark.
Karina: An interesting... theory, Commander. But that's all it is: a theory.
Sisko: That's right. But I'll tell you what isn't a theory: We've tracked the tetryon-emissions back to your warbird and I have about 50 photon torpedoes locked onto it right now.
Dennis Maddalone (Atul) also plays the Guard on the DS9 episode "Shattered Mirror", Transporter Chief Hendrick on The Next Generation episode "Identity Crisis", and Ramos on The Next Generation episode "Heart Of Glory". In addition, he was the Stunt Coordinator on dozens of episodes for both DS9 and Voyager.
Jack Shearer (Ruwon) also plays the role of Ambassador Vadosia on the DS9 Episode "The Forsaken", Admiral Hayes on the Voyager episodes "Life Line" and "Hope And Fear" and the Star Trek: TNG movie First Contact, as well as Admiral Strickler on the Voyager episode "Non Sequitur".
Kira informs Sisko that the Romulans have been moved to habitat level 2, section 47. The number 47 has special meaning in the world of Star Trek, as it is frequently heard in dialogue and seen on computer screens.
The origin of the significance of 47 can be traced to The Next Generation and Voyager writer Joe Menosky, who attended Pomona College in California. There is a club at Pomona called The 47 Society, which claims that "there exists a mathematical proof that all numbers are equal to 47, and that the number 47 occurs with greater frequency in nature than other numbers." Joe Menosky began including references to 47 in season 4 of The Next Generation, and since then it has been seen in nearly every episode, across the Star Trek series.
Cirroc Lofton (Jake Sisko) does not appear in this episode.
Because of the switch made, every appearance of O'Brien following this episode is in fact the O'Brien from 3 hours into the future.