Based on the evolution of a fandom in tumblrscape, Good Omens is on maybe 2.5 times speed, I think? Here’s my reasoning:
1. Posts involving still shots and generalized screaming. This stage normally seems to start immediately and last 1-2 weeks, after which such posts may continue to exist but are generally drowned out by other posts. For GO, this stage seems to have lasted about 2 days.
2. Meta. This normally kicks in after the squee has a couple weeks to percolate, though early meta may appear within a week. For GO, detailed meta began appearing within about 36 hours of the show dropping (possibly less - tumblr’s post structure makes dates hard, and GO’s tag is unnavigable right now).
3. Gifsets. This is a long phase that usually begins once files are generally available. For TV shows, we typically see an uptick for a new popular show after maybe 2-3 episodes, I think? It can take longer if a show doesn’t catch on immediately. For movies, of course, it takes longer to start, and there’s a longer tail as higher quality source becomes available. GO gifsets began hitting my dash at around 3-4 days post-canon, and they ramped up very quickly. This might have to do with available format and the early leakers.
4. Fanart and fanfiction. These typically start about 2 weeks out and often seem to ramp up about 6-8 weeks out, though you might get early sketches and short fic within a day or two of release. The GO situation is complicated by the existence of previous canon - in this case, the book.
4a. The Good Omens TV fandom tag on AO3 was first used on November 5, 2018, probably for this reason. The first work unequivocably based on the TV show and not tagged in anticipation or retroactively tagged with it after it came out was posted on May 31 and is 355 words of Nice and Accurate Headcanon involving the third episode of the show. That’s... a little fast for most fandoms. But we didn’t see the tag really get out of control until a little over a week later.
4b. Similarly, the fanart on tumblr didn’t start hitting my dash until about a week after the series dropped, and it didn’t become ubiquitous until about 2 weeks out.
That’s still awfully fast.
5. Wank. The visible backlash of “how dare all of you like something” hit about mid-June, though there were splashes before. Since Gaiman is on social media, particularly tumblr, most of the wank appears to be of the usual variety thrown at creators deemed reachable. It’s not the wank that’s surprising here - it’s that it came in so fast. We do know that the purity wank crowd has a solid system at this point, but this show is a bit outside their normal target range (as in, it’s aimed at adults). All I can speculate at this point is that this is the new flavor of the old normal pushback that happens whenever any fandom gets “too popular” and the people who aren’t interested forget that we have tag blocking now.
Keep in mind, we’re just at 5 weeks out as I write this. 5 weeks. What even?
Conclusion (or, Further Questions)
So by now it should be obvious that I pulled the 2.5 number out of some random place, because what’s happening here isn’t really quantifiable relative to traditional fandom dynamics. It’s not the way a TV show fandom with a regular release schedule operates, but it’s also not the way a movie fandom with its restricted access operates. We’ve had series drop all at once before - for example Sens8, the various Marvel Defenders series, and Stranger Things. Even Sherlock kind of did this, with its weird, periodic canon drops.
But GO is splashing harder across my dash and on tumblr in general than I saw the Game of Thrones finale do. It’s as if the heyday of Sherlock were compressed from a 6.5 year long thing into a... well, we don’t know yet, do we? Because that’s one the questions: how long will this last? (Another being: Is this just GO being weird, or is this the speed fandom is going to go at now?)
I don’t have the answers any more than anyone else does, but I’m very curious to see what happens from this point forward.