I've seen police missing persons announcements this year (and also received text message alerts, that are not opt-outable or blockable - they get sent to every single person within reach of the relevant cell tower) for people who've been missing less than 24 hours

either the rules have changed

or the 24 hours rule doesn't apply if the person in question

is eg 12 years old or less

has dementia

has just been in hospital for medical issues

etc