Thinking through what you are targeting and whether folks are calling for it at the time is one aspect, though really this depends, what form of advertising are you talking about?
Internet ads you can run immediately, some other advertising can take longer to implement or require special timing. I'm no guru in this arena but for the species I work with I've limited my seasonal advertising (that which can be turned on and off quickly) to when I know the species are either most active or when the bulk of calls come in.
If you are running rather a billboard versus internet marketing, that billboard is designed to have folks remember you on a longer term and be seen throughout town as part of a campaign. We looked into the billboard option with clear channel here years ago, most of the locations were not worth the dollars they were asking, but their goal was to have you seen across the city in heavy traffic areas.
I laugh at the moment remembering asking her (the sales rep) what do they do if I have pigeons on my billboard mucking up my signage?
Received a bit of a blank stare...
Internet, Phone Book, Billboard, Radio, TV, Cards at the Local Stores, etc... all different really in terms of how quickly you can mobilize them and how they work.
Just my .02 but really to me depends on your goal in terms of species and in terms of types of calls (exclusion, trapping, etc...) and so many other cursory factors....
We did a local magazine that goes out pretty wide in the city, to my knowledge no calls came from that and I could have done about 5 years of internet marketing for the cost!
R.O.I.
Important letters!