Hi Zabado,
Youcould fit a timer to turn off the 24volt after a set time. here is a link to one that might work.
http://cgi.ebay.co.uk...&mt_id=635&kw={query}
You would need to buy a cigarette lighter plug and a length of wire (twin) to power the clock. Make sure the polarity is correct, 24 volt + is the centre pin of the plug. Link the terminals you powered the clock from in the back of the unit , 24volt + and - to the input terminals that are switched by the timer( power input terminals ). Wire in
your inverter to the power output side of these terminals.(again 24volt + and -, making sure the polarity is correct,) to the 24volt + and - supply to your inverter.
Set the timer to how long you want the fridge to run, and your off! The timer remains powered while plugged in, but uses very little electric. Sorry if this is a bit wordy, but it might be of help to you if you can do a bit of electric wiring.
Good Luck.