I am feeding a stray cat near my apartment, and each time I feed her, I fill or half fill a disposable bowl of cat food. Sometimes, even after one day the bowl is still not empty, that is, she has not eaten it all. My question is, must I lower the quantity, or can the food stay outside in the bowl for more than one day, without clinically damaging the food (and she could still feed on it)?
Assuming that you are feeding dry cat food and that it is not getting rained on, the food should be fine outside for a few days.
If the humidity is very high, and the dry food is not staying crunchy then you should remove it or lower the amount you are feeding at one time.
For wet cat food (canned) you should not feed more then will be consumed in a single day.