There is no time limit except the statute of limitation for the underlying crime. But you must realize you don't press charges; only the DA can do that. You report the incident to the police and if they think there's anything to it they'll forward it to the DA. Even then the DA can decide not to prosecute.
Misdemeanors in NC have to be charged within 2 years. I gather from your question that the police were not called at the time. Depending on your county, if you want to press charges you would go down to the courthouse and talk to the magistrate. Technically, the District Attorney prosecutes your coworker. But cases initiated by the victim ("peoples' cases") often move forward only if the victim stays in touch with the DA and is a motivated witness.