Ah, despite the admirable variety in timezones for advertisers, it turns out that this is only rolling out in a limited set of countries:
Australia Available
Canada Available
Japan Available
Korea Available
New Zealand Available
United Kingdom Available
United States Available
Weirdly no EU countries...
Cue the usual "EU is killing innovation because of all of those pesky tech and privacy regulations" thread where non-EU citizens and bots try to convince you that all EU consumers are clamoring to get access to this treasure trove of new features they're being "denied" access to.