The point is that Doctor Manhattan didn't get rid of everybody. According to D-Clock, Green Lantern is dead, and probably Hourman too; but "The Button" has the original Flash trapped in another dimension (probably the Speed Force). Sandman, Doctor Mid-Nite and Wildcat are lost to history, as are the original Atom and Starman. However, the latter two have modern counterparts (Ray Palmer, Ryan Choi and Courtney "Stargirl" Whitmore); as do Mister Terrific and Black Canary. In fact, the Metal miniseries just got done explaining how Hawkman has been active in one form or another for generations, albeit without the Justice Society. What's more, the Spectre and Doctor Fate have both appeared in the post-Flashpoint era, and they're each potentially more powerful than the original Green Lantern.
Then there's the current Multiverse's Earth-2, which boasts modern-day versions of the original Flash, GL, Sandman, Atom, Mister Terrific and Wildcat. Did Doctor Manhattan create Earth-2 out of remorse for letting Alan (and presumably some others) die? Is it just an exercise in cosmic probabilities and alternate histories? We're guessing Doomsday Clock won't answer those questions, let alone travel to yet another Earth; but by implication does that mean Doctor Manhattan doesn't know the details of the Multiverse? How might that affect his perspective?
It's all part of our larger concern about the extent of Doctor Manhattan's powers. Nothing in Watchmen suggested that he could time-travel. Instead, he experienced all of his life all at once (muddied by some tachyon interference around November 1, 1985, of course). Now, as per Page 2, apparently he's come to DC-Earth from Watchmen's November 1985. Upon arriving – we're thinking sometime between the end of Crisis On Infinite Earths in 1985 and Flashpoint in 2011 – he saw a planet full of superhumans, and decided to change its history. This doesn't contradict our longstanding theory about the intersection of Watchmen and DC-Earth's respective timelines, although it doesn't confirm any of our suppositions either.
Speaking of confirmations, Dr. M's discussion of Carver Colman on Page 23 leaves plenty of room for our theory that he posed as Colman until the actor's death in 1954. At the very least, we now know that he watched The Adjournment being filmed in April 1954, and beheld Colman's corpse in June of that year. Either way, it seems likely that he knew Jonathan Law, who otherwise would have been the Golden Age superhero Tarantula.
Doctor Manhattan returns in person on Page 14, in the middle of a black-and-white tiled floor not unlike that of The Adjournment's chessboard. (Page 27 connects the two explicitly.) On Page 15 he prepares to teleport away all the Watchmen natives, virtually ignoring DC-Earth natives Batman and Joker. It's a bit reminiscent of the Batman/Joker scenes in May 1985's Crisis On Infinite Earths issue #2, when the time-traveling Flash pops into the middle of the Darknight Detective apprehending the Clown Prince of Crime, and promptly disappears. The result in both cases appears to be a very confused Batman and Joker.
Once again Pages 16 and 21 utilize the "teleportation perspective," which on page 21 appears to be from Ozymandias' viewpoint.
On Page 17 we see that Dr. M and company must be literally on the other side of the world, since it was dark in Gotham City and daylight where they are. Likewise, the group's trip to Los Angeles for a midnight showing of The Adjournment (Page 23) suggests that it was between 3:00 and 4:00 in the morning on the East Coast. Dr. M's "in the middle of something" declaration (Page 17) implies that he's waiting for the results of whatever experiment he's running. We don't read that to mean he's still messing around significantly in the DC timeline, although certainly he could have been meddling in the very recent past.
Doctor Manhattan's Page 18 mention of the security cameras at the Rockefeller base may be helpful in dating the Mime & Marionette robbery depicted in issue #2. Watchmen issue #4 establishes that when he and Laurie moved into Rockefeller in 1981, Laurie was concerned about their privacy. Granted, there's 11 years between 1981 and Rorschach freeing M&M in 1992, but it does mean that M&M's robbery can't have occurred any earlier than 1981.
The more important takeaway may be Dr. M's "choosing" to save Marionette's unborn child. Although Dr. M can't see more than a month into his own future, this may suggest that Watchmen's world can still be saved. Either that or Marionette's child grows up to be an important person on DC-Earth. (We'll take "ancestor of R.J. Brande" in the office pool.)
Page 22's trip to Washington, D.C. is a clear callback to the 1977 police strike riots on Watchmen's Earth which led to its Congress banning all masked crimefighters.
We couldn't find a "Revival Theater" (Page 23) in Hollywood on this Earth, but Revival Hub LA is a central source for classic movies in Los Angeles.