I was using Cairo-dock and the shutdown applet allows for a timer to be set before actually shutting down! i think this would integrate with the shutdown button on cinnamon really nicely. I wasnt keen on cairo dock as it was too busy and didnt fit with cinnamon too well but the features there are really smart (like drop box)
so yea, a nice simple ShutDown -> "Delay shutdown for:" then have a slider like the audio track position where you can set for 30mins, 2hrs or 6? whatever!
in the past on windows i used a more complex shutdown timer with great success as i have a fairly average internet connection and downloading large files can take a good few hours which is fine but i look at the time left and think.. hmm this should only take about 1 hr so il set the timer for 2 just for good measure and go to bed / go to work and feel confident the computer is off and not wasting energy
it also helps for some users i suppose who use linux for TV and might want to use the shutdown like a tv sleep function