Sometimes when a user has tried a few incorrect passwords in rapid sucession they may get locked out of their account.
The default time for this is 1 HOUR. If a user contacts your library for support and wants to log in right away, you can clear this up for them.
Click the box in the row containing their username and click the "clear flood" button. You should see a success message and the user should be able to log in immediately.
Encourage them to click the link to request their password if this happens again, and feel free to explain why this security measure is in place.