First hour
The operators publish a signed notice with the new we the north market mirror and, usually, the date the old one stops working.
First day
Reference sites check the notice and update their lists. Copycat posts with fake "new mirrors" appear at the same time.
First week
Most visitors move over. The old address may still work for a while, then stops responding.
Afterwards
Old posts with the retired address keep circulating for months. Lists with dates help you recognise them.
Most confusion around a WeTheNorth mirror change happens in the first day; wait for checked lists if you can.