The latest from longtime SLIFF favorite Chris Grega (“Rhineland,” “Game of the Year,” “Sound of Nothing”), “35 Days” is a mockumentary riff on a subject that the local filmmaker knows all too well: the scramble to complete a movie on a tight deadline and nonexistent budget. St. Louis indie film director Eric Cutter (Travis Estes) — an exaggerated but sympathetic take on Grega — decides to complete his long-abandoned third feature, “Gunman,” as a tribute to his friend Sam Harrison (Steven J. Heffernan), an actor in the film who recently died. To accomplish the task, Cutter must reunite his quarrelsome cast and crew to finish the movie that derailed their hopes and dreams a decade earlier. The problem: They have a scant 35 days before the film is set to screen at the St. Louis International Film Festival. By turns funny and sad, absurd and poignant, “35 Days” will amuse local film insiders with its knowing references and cameos, but the film also works on a much deeper level, providing a surprisingly nuanced portrait of a talented creator unfairly challenged by a lack of resources. Repurposing footage from “Amphetamine,” his first feature, Grega also provides a touching valedictory to Heffernan, who, like his character in “35 Days,” died far too young.