It's been suggested to me if the Python isn't eating then to leave the mouse in the terrarium over-night. Thus you probably needn't worry about the duration the food is in the tank for your reptile. However I would remove the mouse in the morning if your snake hasn't eaten the rodent, then try to feed he or she again after a few days.
Pyth
Pyth, your advice is good for live prey, but I think the OP was asking about F/T.