I was updating my security info, where it lists a backup email address. Because I had closed that backup email account previously, I wanted to remove it as my backup. It took me to a page stating the following:

I don't have my security info any more

If you ever lose access to your account, your security info helps you get back in. Update this info to help keep your account secure. It will take 30 days for the update to take effect. The waiting period makes it harder for a hacker to lock you out of your account with just a stolen password.
 
What does the sentence mean: It will take 30 days for the update to take effect.
 
What "update" is it specifically referring to? And why does it take 30 days to take effect?
 
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