Scheduling a terminal command or script file to run daily at a specific time Mac OS X

As @TheDarkKnight points out, cron has been deprecated in favor of launchd.

To use launchd, save the following as com.example.volume.plist in ~/Library/LaunchAgents/:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
        <key>Label</key>
        <string>com.example.volume</string>
        <key>ProgramArguments</key>
        <array>
                <string>sh</string>
                <string>-c</string>
                <string>set volume 1.7</string>
        </array>
        <key>StartCalendarInterval</key>
        <dict>
                <key>Hour</key>
                <integer>23</integer>
                <key>Minute</key>
                <integer>45</integer>
        </dict>
</dict>
</plist>

then run launchctl load ~/Library/LaunchAgents/com.example.volume to start. You can force the task to run immediately via launchctl start com.example.volume.

If you prefer to have it run as root, save to /Library/LaunchDaemons/ instead.