What is the law on schedule changes, does an employer have to tell you within a certain amount of time can they even change schedule after being posted?¿

There is no law on schedule changes so no, your employer is not required to give you any advance notice of a change.

Where would I find that in the actual labor laws?¿

Where would I find that in the actual labor laws?¿

Beth stated there isn't a law, so you won't find one

so I could go in for a scheduled 4 PM shift but at 3:59 my boss changes it For me to be in at 3 PM then I get fired for being late and theres no law against that?

so I could go in for a scheduled 4 PM shift but at 3:59 my boss changes it For me to be in at 3 PM then I get fired for being late and theres no law against that?

No, it's called at-will. You can be fired for anything not prohibited by law and thats not one of them.