The Minuteman Intercontinental Ballistic Missile (ICBM) heading for Star City is shown in powered flight complete with its initial stage 1 booster attached minutes from detonating. The 1st stage booster is ejected approximately 60 seconds after launch and the powered flight stage is complete by the time the warhead re-enters the atmosphere (after approximately 3 minutes after launch). At the point the ICBM could be seen by the residents of Star City it would be in it's ballistic phase (falling out the sky really fast) meaning Felicity and Curtis would not have been able to redirect it the way they did, the only way to stop it would have been to shoot it down.
While Oliver is giving his encouragement speech on top of the taxi, one can see a Canadian flag flying from the facade of a building. This is due to the show being filmed in Vancouver, British Columbia.
Felicity says that the closest ICBM was headed to Star City from Warren Air Force Base in Colorado. IF she is referring to F. E. Warren Air Force Base that is in Cheyenne, Wyoming and not Colorado.