Conditional Formatting highlighting a blank cell

I have a mock up sheet attached, I need Column C to highlight only cells that have a value. Column B will have the values change based off a formula. Some numbers will be negative so I just want Column C to say ON TIME for those. It works great except the cells in Column C the conditional formatting applied that does not have a value highlights the cells Red. How can I make the cells not show Red? I just want them blank if a value does not exist. Thanks,