Ok, well, here's how you would make launchd run at 2:05 p.m.
Copy this using a text editor and save it as ~/Library/LaunchAgents/com.tjluoma.quit-at-time.plist
<?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.tjluoma.quit-at-time</string>
<key>ProgramArguments</key>
<array>
<string>/usr/local/bin/killMathematica.sh</string>
</array>
<key>StartCalendarInterval</key>
<dict>
<key>Hour</key>
<integer>14</integer>
<key>Minute</key>
<integer>5</integer>
</dict>
</dict>
</plist>
Note that you'll need to logout/login or use launchctl load ~/Library/LaunchAgents/com.tjluoma.quit-at-time.plist
Now, the /usr/local/bin/killMathematica.sh
line could point to whatever it is you want to run: an app, an AppleScript, or a shell script.
The easiest solution is a shell script:
#!/bin/zsh
APP='Mathematica'
PID=$(ps cx | fgrep "$APP" | awk '{print $1}')
# if $APP isn't running, then just exit already
[[ "$PID" == "" ]] && exit 0
# if we get here, then $APP is running
# tell it to quit using AppleScript
# if this exits properly, the script will exit too
osascript -e "tell application \"$APP\" to quit" && exit 0
# if we get here, AppleScript didn't work, so let's try
# sending the app a 'kill' message
kill -QUIT "$PID" && exit 0
exit 1
# EOF
save that as '/usr/local/bin/killMathematica.sh' (or wherever) and make it chmod 755
Test it out and see if it works.
Now that I've given you the answer to the question you asked…
Here's a better solution: use Keyboard Maestro. It's much easier.
How easy?
http://images.luo.ma/Keyboard_Maestro_Quit_at_Specific_Time-20120717-195546.jpg
Boom. Done.
No launchd. No cron. No AppleScript.
(I had to use VLC instead of Mathematica because I don't have Mathematica installed.)