“The First Day of Shooting” is a grungy documentary about four friends in their 20s who set out to make a short, no-budget horror film. With smiles and laughter, they recall their giddy, high-school short “The Dream,” made with boundless energy, no money, and ketchup for blood. The new short’s working title is, aptly, “The Dream Part II,” and will be directed by “The Director,” fresh from film school. But, in interviews and in action, it becomes clear that, for most of them, the goal isn’t so much to finish the new project as it is to reclaim, however briefly, their happy-go-lucky adolescence. Even the short film’s writer is skeptical of art’s ability to do more than entertain. Is “The Director’s” greatest obstacle cameras and lighting, or that his friends can only muster a single, one-night burst of enthusiasm? As they chat between takes, “The First Day of Shooting” reveals much about that time in our 20s when we decide if we pursue childhood dreams, or discard them in favor of adult concerns. Whether they finish the movie or not, The First Day of Shooting provides commiseration and catharsis for artists everywhere struggling with a lack of willpower, either in themselves or those around them.