How long does a carrier unlock take?

I just got this mail from my previous provider. Unlock Code: PLEASE READ BELOW

Thank you for taking the time to contact T-Mobile. 24 hours after receiving this email, follow the below instructions for unlocking your T-Mobile iPhone.

If you have a non-T-Mobile SIM card, follow these steps:

If you have a non-T-Mobile SIM card: 

1. Insert non T-Mobile SIM Card

2. Complete the setup process.

If you will be using your T-Mobile SIM card follow the steps below:

1. Back up your iPhone using iTunes.

2. When you have a backup, erase your iPhone.

3. When you see the Welcome screen, connect your device to iTunes.

If successfully unlocked, the message Congratulations, your iPhone has been unlocked will display. Additional information for unlocking Apple iPhone devices can be located athttps://support.apple.com/en-us/HT201328

I called them and they said i was able to use my sim. But it still doesnt work. Now they are blaming apple for it to take so long. How long does a carrier unlock dure?

kind regards