[Rjevski]

iPhones are not really "locked" like traditional phones are when you need to submit an unlock code (essentially a password) to the modem to allow it to connect to non-whitelisted networks.

iPhone modems are unlocked by default (so a locked iPhone will still connect and get internet access just fine) but the OS will check-in with Apple and submit the first digits of the SIM's ICCID to check if it's allowed to operate with such a SIM.

I would thus expect an unlock to be immediate, unlock request sent to Apple, a row is updated in the locked devices database, and next time the phone checks in, it gets a positive response and the OS lets you proceed. Most likely it's the carrier's stupid & outdated systems that only submit unlock requests in batches every X days or so. Could even be manual with a spreadsheet being written up by a poor slave somewhere abroad.