So I'm working on a book (the plan is to make it a series) covering the lives of a bunch of immortals (vampires, werewolves, and other such creatures secretly living among humanity). It starts in 1990, but will gradually advance through the years getting closer and closer to modern day, and a recurring part of the story is how their efforts to stay a secret keep getting harder the more advanced human technology gets. This will play a massive role at the climax of the series as I envision it, though obviously for spoiler reasons I can't say more. My issue is I'm not sure how to handle the passage of time here. Should I have it be like Harry Potter but on a longer timescale, where one book will cover a story arc that takes multiple in-story years to conclude? Should I tell stories that take place on a smaller timescale and skip ahead massive amounts of time between them? Some other method that I can't think of at the moment? I'm having difficulty wrapping my head around the pros and cons of each method, so I was wondering if anyone had any advice on how to decide how to tackle this. If it helps, for context, the story is heavily implied to be the main character writing a sort of memoir of his life and his adventures with his friends years after the fact.