Password expiration issue (not triggering)

Hello,
I’m trying to better understand how the password expiration logic works in this plugin.
When setting a value (for example, 3 days), how is the expiration actually calculated? Does it:

• Count from the user’s registration date?
• Start from when the plugin/settings were activated?
• Or depend on the last password reset date?
  
  I tested this with an older user account (registered over 2 years ago), but the password reset was not triggered immediately, which made me question how the logic is applied.