How long does it take to enable and disable FileVault on a 1TB internal SSD with 90% full capacity?

That is because that is the time needed to change the setting, only.

The actual conversion from encrypted to not or the other way around takes all afternoon to overnight of background 'awake but not too busy' time. It can not be changed again or cancelled until completed. While most operations can proceed, some operations (such as software updates) are blocked.

MacBook Pro models with T2, and MacBook Pro models with Apple silicon, are already operating with encrypted internal storage, and you can’t do anything about that — other than providing a password of your choosing, which is what happens when you are selecting a FileVault password here. And AFAIK, all MacBook Pro 16” models either have T2 or have Apple silicon.

Which means enabling encryption is — to quote Apple — “immediate”. It’s already encrypted.

See page 121 here: https://help.apple.com/pdf/security/en_US/apple-platform-security-guide.pdf

RAMSLOT wrote:

Your post conflicts with Grant's post, correct?

Grant correctly describes the behavior on Macs prior to T2, and the current FileVault behavior with external storage absent hardware encryption.

<< How many seconds or minutes will it take for File Vault to be turned on / enabled? Same question for disabling. >>

why are you asking about this?

When you are logged in with your userid, the data are completely accessible to you in every case.

When you are just trying to brute force read encrypted from outside, without your user-id, data reads return gibberish.

There is NO measurable delay in reading or writing due to your data being encrypted or not.

RAMSLOT wrote:

Is that for enable? Disable? Both combined?

On modern Mac computers, which seems to include your MacBook Pro 16″, encryption is always enabled. It can't be turned off. But on these computers, if FileVault isn't enabled, then a password is saved so that the system can automatically boot. If you enable FileVault, it merely deletes this password. Then, in order to boot, you have to supply your password.

Therefore, enabling or disabling FileVault should take only the amount of time required to write or erase about 32 bytes of data. But full disclosure, I haven't actually tried this. I can't remember the last time I used a Mac without FileVault enabled. It looks like it came out in 2003, so it's been at least two decades. Haven't had any problems or performance complaints in that time.

etresoft wrote:

...Therefore, enabling or disabling FileVault should take only the amount of time required to write or erase about 32 bytes of data...

Though it’s slightly more complex than that, as macOS chats with the secure enclave, requesting it decrypt and then encrypt the volume encryption key using the newly-generated key encryption key.

Since the volume encryption key itself doesn’t change, there is no overhead from encrypting or re-encrypting the already-encrypted volume.

And also no decryption and re-encryption overhead should the FileVault password eventually be changed too, rather than necessitating volume-wide decryption and re-encryption passes. Just the keys get de- and then re-encrypted.

The overhead of all this key shuffling is negligible, as processing the whole volume is avoided.

See page 120.

Approximately 13 microseconds.

RAMSLOT wrote:

Are you the Author of that excellent analysis software by the same name?

Yes.