We were asked just this question yesterday–twice, as a matter of fact. As usual, there is no hard and fast answer to this question. I’m loathe to say it, but our typical answer is “it depends.” It depends on the market, channels, means of entry, business requirements, etcetera.
In an ideal world, you’d plan your entire promotion taking into consideration the full range of influencing factors. However, that doesn’t always work. For instance, we planned out the timing of contest yesterday with a client. In this case, media buys and television programming directly influenced the duration of contest. For this contest, the entry period will be no more than four weeks.
With another project, we have the luxury of an adequate amount of advance planning. As such, the contest length can be determined specifically by the tactical requirements of the campaign. For this contest, which is primarily retail-driven, we’ve recommended a 60- to 75-day contest period.
Empirically, we know that contests should run 60- 90-days, but generally we see interest and entries wane after the 60 day mark.