How long Is the Food Good for?????

If i kill a mouse, through it in the cage, about how long is it good for before i should take it out. i know thay get realy hard and start to rot

if its not gone over night throw it

best thing to do is put the snake and mouse in a shoebox together with nothing else. No risk of snake eating the substrate which can get impacted and cause bad health issues. Also speeds up the feeding.

For starters, don't throw it in the cage, move the live critter to another enclosure [like the shoebox mentioned above, or a plastic tub] give it a water bowl, and add the snake-chow. Shut the lid and give your pet some privacy. If there's still snake-chow in a few hours [overnight max], toss the snake-chow out and try again in a few days.

Remember that a dead mouse is meat, but more unstable ... the contents of the gut are still in, and will start rotting very quickly. While corns are fairly hardy, captive snakes live in fairly sterile conditions, so don't ask for trouble by feeding chancy food.

An afterthought: You refer to killing the mouse ... I hope you're referring to a captive-bred/kept mouse and not one from a mousetrap in your house ... wild mice can have some nasty parasites/diseases that you really don't want anywhere near your pet.

Lots of good info here too:
http://www.cornsnakes.com/forums/showthread.php?t=28341
http://www.cornsnakes.com/forums/showthread.php?t=28342
http://www.cornsnakes.com/forums/showthread.php?t=39306