From Google's universal navigation
Simply click on the More link and then on ScheduleOnce. Since you're already signed into your Google Apps account you will instantly have access to your ScheduleOnce account and no login will be required.
Direct access
Type your organization URL: http://yourcompany.scheduleonce.com
Replace "yourcompany" with your organization's name or the name chosen by your Google Apps Administrator when ScheduleOnce for Google Apps was installed.
If you are not already logged into your Google Apps account you will be prompted to login with your Google Apps user name and password.