Weapon Running Time

AKA Time to Impact.

Because all kinetic weapons have a finite speed (along with most energy based ones) they take time to get from attacker to target. Even light takes 8 minutes to reach Earth from the Sun.

Sometimes this becomes a plot point. When a weapon takes over 30 seconds to reach a target, it allows things to happen. As in self-destructing the missile or attempting to.

May well involve a Magic Countdown.

Examples of Weapon Running Time include:

Film

In Tomorrow Never Dies, Bond has to get an aircraft clear from an Arms Fair before a Tomahawk hits the place.
The Hunt for Red October has several scenes with torpedos inexorably closing in on the sub. Usually includes the first officer stoicly counting down the time to impact with his stopwatch.

Literature

In Eagle Strike, Alex has 90 minutes to stop the nukes launched by Cray near the end of the book.

Live Action TV

In Blakes Seven plasma bolts had running times, allowing the force wall on Liberator to be activated.

Tabletop Games

In Harpoon missiles and torpedoes move set distances during engagement turns and may take over 10 minutes to reach a target.
Torpedoes in Battlefleet Gothic move a set distance (usually 30 cm) every turn, which means that at long ranges they're more useful for limiting enemy movements than actually attacking.

Video Games

Modern games often incorporate a tiny, practically invisible delay between firing and the slug hitting your target.
Many a game involving Hot Sub-On-Sub Action.
The first scene in the Call of Duty 4 mission "One Shot, One Kill" is a sniping mission. The target is so far away that the bullet will take over a second to reach him and your CO tells you that you need to account for the Coriolis effect in your aim.
- Later, during "Ultimatum," the bad guys launch ICBMs toward the Eastern Seaboard. "No Fighting in the War Room" becomes a Timed Mission to take the control room and enter the missiles' destruct codes.

Real Life

Torpedoes generally go around 50 knots. When launched at a target 2.5 nautical miles away, a torpedo will take 3 minutes to reach a target, allowing a sub time to "clear datum."
Nuclear missile from the US to Russia, about half an hour. From Russia to the UK, about ten minutes. From Cuba to the southern US, under five. Welcome to nuclear strategy.