I once contacted Kraft Foods, maker of Philadelphia Cream Cheese, and asked this question. They said 2 hours. I assume they're worried about being sued if someone gets sick, so they were probably conservative. I'd say 3-4 hours tops.
Thanks so much!
Do you mean like sitting on the counter? I've left it on the counter up to 3 days, EVERYTIME. No one has ever gotten sick. And htese are my kids eating the Red Velvet Cake it was covered in.