Five Minutes to Midnight

Five Minutes to Midnight is a WatchmeX arc chronicling The Dramedian's journey 30 years back in time using the Watchback Machine in order to detonate a nuclear bomb on New York before any costumed heroes were old enough to oppose him. Rorschach, Nite Owl II, and Silk Spectre II follow him back in time, and ultimately team up with younger versions of themselves (as well as Dr. Manhattan and The Comedian).
The two teams of heroes split up to search for the bomb hidden somewhere in the city. The Dramedian constantly taunts that only five minutes remain until the city is destroyed, thus the title of the arc. It is unclear how the events of this series were possible in this timeframe, although it is possible that Teenage Dr. Manhattan used his powers to slow down time.
Halfway through the story arc, The Dramedian reveals that they had all traveled into the past of an alternate universe by mistake. This is widely believed by fans to have been a last-minute attempt to make up for the storyline's disregard for established canon (all of the Watchmen characters being the same age and becoming heroes as teenagers, the lack of acknowledgment of older heroes such as Hooded Justice, etc).