Parental Controls Through Terminal
You can change /Library/Managed\ Preferences/Username/com.apple.familycontrols.timelimits.v2.plist under the key time-limits there are 2 dictionaries you may need to consider :


weekday-allowance
weekend-allowance


Both have a key "secondsPerDay" you may change. 

You may edit the .plist by converting it to XML using sudo plutil -convert xml1 theFile and then edit it with your favourite command line editor.