The Center For Responsive Politics Candidates for all federal, state and local offices are supposed to have automatic access to the lowest rate on a television or radio station's rate card, in accordance with a Federal Communications Commission requirement. However, this rule only applies to the 45 days before a primary election and the 60 days before a general election. The law eliminates negotiation, which results in one less job for the media-buying agency. It is to the advantage of a campaign to be the first one on the air, because then they're the first ones to have their name recognized. Starting a campaign early is a strategically good idea, but most generally wait until there is a lot of people advertising at the same time.
Budgets affect more than timing.
They can have an impact on other aspects of an ad agency's campaign planning. Very often, the candidate doesn't have the money. So, you are constantly having to adjust based on the candidate's ability to raise funds. If you know he is falling behind, and he is not going to have enough money, you may have to adjust the midpoint of your schedule to maintain what you feel you will need at the end.