I don't own an Airtag or iPhone for that matter. I wonder how is it supposed to not raise a false alarm if you are travelling with someone who has an Airtag - e.g. by car or by train. Now imagine changing trains at the same stop with someone who has an Airtag with them (this is s typical situation in commute with public transit).

So I figure it takes a longer time for the devices to be close to each other to raise an alarm.

Now back to the mail thief, I suppose an hour or two is enough to catch them.