Try the following. This should reduce the time to take backup.
1) Rename the file C:\Program Files\Common Files\Cisco\Logs\stiBack.log to C:\Program Files\Common Files\Cisco\Logs\stiBack_OLD.log
2) Restart the Cisco IP Telephony Applications Backup service from the Services control panel (ie. Start > Programs > Administrative Tools > Services).
3) Verify the configuration with the Backup Configuration utility and attempt to run the backup again.