Concept: Patreon-supported webcomic whose basic reward is "see today's comic tomorrow" – i.e., an apparently useless joke reward that grants access to a series of Patreon posts which update one day behind the public-facing site's update schedule.
The non-obvious twist is that the Patreon version of each page takes place one day later in-universe as well; at first this is reflected by small details, e.g., a timestamped video feed that's visible in the background being dated 24 hours later, but the differences soon become more pronounced due to events not lining up in quite the same way.
It's ultimately revealed that the Patreon comics take place in an alternative universe in which the story's inciting incident occurred 24 hours later than it did in the prime timeline. This culminates in an ending where, in the prime timeline, the main characters are able to prevent a world-altering catastrophe, albeit at great personal cost, while in the alternative timeline, they're exactly one day too late.
















