Thousands of exhibits showing how sundials work, or how any other non-clock time-keeping mechanisms work, would immediately reveal something is amiss.

The number of people that would set their microwave timer for 1 minute at that exact moment and see that it finished and see that it was 2 minutes later would be significant.

The number of text conversations where people send half sentences constantly, time logs.

Any chatrooms chat logs. Just all suddenly missing a minute. During heated debates.

There are so many non-clock related instances of time tracking that exist within rigid time frames, globally…

Youd have dozens of social media posts showing the same anomaly. At the same time.

I give it ~3-4 hours before it is trending globally, maximum.