Hello everyone. My question here pertains to the use of devices in the vein of "________ Years Later" with regards to a novel. I've seen long gaps in the narrative used exceptionally well (I Am Legend comes to mind), and I've also seen them used terribly, destroying the flow and momentum of the story. This may be far too general of a question, but what are the keys in the setup and pickup that allow these to be implemented smoothly, without jarring the reader? How much can change?