Is it better to apply earlier or later if you have a low GPA and are applying to college?

I'm not really sure what you're asking. You're supposed to apply about a year before you intend to go to college, and while there is some leeway with that you don't want to apply too early (e.g. in your junior year of high school) or too late (e.g. summer after senior year if you want to go in the fall). You also need to make sure you don't miss application deadlines. Regardless of GPA, missing a deadline never looks good or helps anyway.