Ad flight: The total length of an advertising campaign.
There is no standard time frame for how long a certain ad can run. Generally speaking, however, the same ad tends to lose its impact over time as it saturates the market and people first get used to seeing it and then began tuning it out.
Commercials for automobiles are a perfect example. Slogans for particular car companies are routinely updated to avoid becoming stale. Most advertisers update their ads periodically with fresh content and/or new slogans, even if the actual product/service remains unchanged. People respond to new things and tend to ignore familiar things.