The Apple ID "example@email.com" cannot be used to unlock this iPhone Recently I bought a second hand iPhone 8. When I'm trying to unlock the device It shows this error:
The Apple ID "example@email.com" cannot be used to unlock this iPhone


Previous user deleted this device from "find my iPhone" service (But still it shows "Erase requested 1hour ago")


How can I register my device under my apple ID? 
Do they take more time to erase a device from the database ?
Apple’s activation servers are generally instant. I’ve gone through the official process maybe 20 times in the past two years for work, and it has never not worked within 1 minutes let alone waiting 5.

Here is the official guide and link for the previous user to remove that lock:


https://support.apple.com/HT201365


Activation Lock is part of the iOS Activation status here:


https://www.apple.com/support/systemstatus/


So if you believe it’s failing, the instructions there are correct - contact Apple Support directly. The only thing I can add, is Apple doesn’t tell you the full email of the previous owner, so unless you have the passcode, you won’t really know which email is “example@email.com” above. 


How exactly are you connected to the internet from the device to try and unlock / activate it?
Do you actually know the email some other way or were you putting something hypothetical in the question?