There is a limit to the number of tries a person has to log in to the backoffice of the store. That limit is configured on Utilities > User Accounts > Configure. If a person attempts to login more than the specified number of times then that user will be locked out of the system and a user with Admin permissions will need to reset the ability for that user to login again.
There is a link on the login screen where the user can request an email to reset their login info. So if the user tries once or twice and and doesn't get in they should use that link to get the password reset email, if they don't then they will be locked out. There is no timeout on the lockout, if you are locked out, you are locked out until a user with Admin rights resets the retry limit for that user.
If you are the only Admin on your store then you will need to contact your host to have them re-enable the login. If they are a ShopSite partner then they can contact Shopsite for assistance if they need it. If your host is not a partner then you can purchase a support incident at http://www.shopsite.com/support_pricing.html.
Note that this is a security feature so it is not a simple matter to reset the password if the Admin user is locked out.