How long does it take for antibiotics to leave your system?

That differs for different antibiotics. For some it's only hours, that's why you need to take them several times a day. For others it can be days. It also matters if the doses are oral or intravenous. Talk to your pharmacist if you want to know about a specific one you have been taking.

Depends.: Half-life of penicillin is a couple of hours; that of Azithromycin - several days. Other meds are in between.