Alexander Burns, "Obama super PAC to advertise in Ohio", Politico 2/28/2012:
The pro-Obama super PAC Priorities USA Action is poised to start airing ads in Ohio, according to a source monitoring the 2012 air war.
Priorities USA has already put down $61,530 in the Columbus media market for a flight running March 1-6. That's a small sum compared with what Republican groups are spending — the Romney super PAC Restore Our Future has a $1,130,750 TV and radio flight running Feb. 27-March 6 — but it's probably going to be enough to drive a narrative Democrats are looking for.
When I read this, I interpreted flight as referring to a sort of flock or swarm of political ads, connected to sense 8. of flight in the OED, "A collection or flock of beings or things flying in or passing through the air together". That's the sense behind the phrase "a tasting flight", in which flight is a calque for French volée (the etymological ancestor of volley).
But apparently I was wrong.
AdGlossary defines Ad Flight as "The duration of time for which an advertising campaign is live". And other examples on the web are consistent with this meaning, e.g. "DNC Launches New National Cable Ad Flight for 2010 Congressional Cycle", Stimulating Broadband 9/12/2010:
Allen reports the spot will run as a one week flight, while Meckler states the the ad will run for "several days."
Or Tobe Berkovitz, "Political Media Buying: A Brief Guide", 1996:
Known as flighting, decisions must be made to determine when the advertising schedule will be aired.
Few campaigns can afford to run television and radio flights continuously from the start of the campaign until election day. […]
Flighting is the third method of creating an advertising schedule. The phrase advertising flight describes the time when commercials are aired. When flighting is used in relation to a scheduling technique, it refers to a method that has advertising going on and off the air. The advantage of the flighting technique is that it allows a campaign that does not have funds for running spots continuously to conserve money and maximize the impact of the commercials by airing them at key strategic times during the campaign.
Frequently when flighting is employed, radio or cable TV will be used to supplement the advertising campaign during the times when television commercials are off the air. […]
The media buy begins with the selection of specific programs and stations. All decisions for how many spots to place within each program or daypart are done on a week by week basis. An advertising flight consists of a specified number of weeks.
Or again, Nicole Meade, "Political and Issue Advertising", 5/31/2011:
Experience says in retail media buying and planning one must contact stations, request avails and notify stations of the client, flight dates, and demo. […]
Political windows are one unique aspect to political media buying – 45 days before a primary race the political window opens up and 60 days before the general election the window reopens. During that time the stations must give candidates the lowest rate a station has to offer for a specific time period. When stations send candidate cards they must have the various levels of rates that will clear. The lowest rate is supposed to go to the candidate if the flight falls into the window.
So maybe this usage is really more closely related to OED sense 6.a. "The distance which a bird can or does fly" or 6.b. "The distance to which a missile may be shot" — even though these refer to space rather than time.