4 Spots a day = 120 spots per month
Trailers contain the most information about a movie. They usually show moments from several scenes in the film and run the gamut in terms of emotion or mood. Full trailers also show off the cast more than other previews.
Movie trailers generally fall into three overlapping categories that tend to paint with ever more refined brushes. Moving from broadest to narrowest, these are Genre Trailers, Story Trailers, and Star Trailers. While each take different approaches, they have common threads.
Although 15-25 minutes is the most common length of previews, there is a tremendous amount of variation. So, this is only a rough estimate