Lightning didn’t actually wait for her to answer, just leaned in and declared in an ominous voice, “Two years. And you’re lucky, too. Other creatures have some of their feathers for life. If a griffon loses their guide-feathers, they just won’t be able to fly straight ever again. Or even get off the ground, in some cases. Ponies regrow all of them every few years, but… that is not an excuse for bad care.” She pointed with one hoof. “See here? This feather is broken at the end. It’s stuck in your wing, making it itch like crazy I bet. The new one will push it out, but not before it gives all the feathers around it a chance to get infected too. Is that what you want?”