The user above is correct. There are up to two AFM 3 Core models queued for download when you enable Apple Intelligence. When you disable it, local models are likewise queued for deletion. They are not deleted instantly. Both download and deletion are async tasks handled in the background.
The time it takes depends on how many other storage management routines are already queued. Here are a few tips to hasten that process:
1. After disabling Apple Intelligence, reboot the machine.
This will (A) clear maintenance tasks from the queue which complete more quickly pre-login, and re-queues the all remaining background storage routines based on configs which can bump the deletion task higher in the queue.
2. Open a terminal and run
sudo sysctl debug.lowpri_throttle_enabled=0.
This removes I/O throttling of background storage management tasks (spotlight mdstore indexing, Time Machine snapshots, etc). The setting is cleared on reboot or when running the command sudo sysctl debug.lowpri_throttle_enabled=1.
3. If you’re on AC power, open a terminal and run the command
caffeinate -ism -t 24*60*60.
This disables idle, system, and disk sleep for 24 hours to ensure the computer stays awake allowing background storage management daemons to continue. You can turn this off by closing the terminal.
4. Open Settings > Network, click Details for the active connection and turn on “Low Data Mode” temporarily.
This trick is used to prevent AFM 3 Core models from being re-downloaded during manual deletion, but some users have reported it speeds up local model deletion as well. (This sounds like coincidence to me, but you can try it.)
The user above described the official supported method. I added links in a separate comment which include the alternate manual process of deletion. I would suggest using the official method first.
ETA: I don’t know what I expected.