What does it mean to set the SMS to be saved for two minutes on Apple's mobile phone?

It means that after two minutes, the system will automatically clear some short messages.

Apple's mobile phone saves information permanently by default, which means that as long as the user does not manually delete the text message, the text message will always exist in the mobile phone.

If the retention time is set to permanent, it will take up a lot of memory over time. If you don't want to manually clean up short messages, you can change the retention time of short messages, and some short messages will be automatically cleaned up after the expiration.