A film industry slang term. Used as a way to tell actors and crew to hurry up as natural daylight wanes. Since the sun's position and quality changes throughout the day, sunlit shoots can be challenging to match later in editing, so it's important to get scenes done efficiently. This phrase is often used jokingly indoors to spur on the film crew.
Get your rubber masks on and get back into the swamp... we're burning daylight!