When the 5X went out, xiaomi put a 300 hours delay on bootloader unlock requests which was very annoying. I just tried now with a "new" phone (2 years old phone that was still new in box) and now the bootloader unlocks immediately.
A sim card registered to xiaomi "find my phone" service and with active 3g/4g data connection is still needed though
A sim card registered to xiaomi "find my phone" service and with active 3g/4g data connection is still needed though