OS X: Schedule Launchctl to quit application at certain time
One of these two methods should work, but I admit I have not tested them: 


Either you could write an AppleScript a la


tell application "Caffeine" to quit

put this in a file, then either launch the file from an osascript command or  put it into Script Editor and save it as an application and launch that as a an app


or you could use the good old killall command. You would have to lookup the name of process of the Caffeine process and send it a 

killall Caffeine


command, assuming that the process name of the Caffeine app is Caffeine (check  it from the Activity monitor or the ps command)