The full moon occurs when the Moon is directly opposite the sun at which point it is 100% illuminated by the sun. If it is only 99% illuminated, it isn't a full moon. It passes in about three hours and it is gone. read more
However to the unaided eye it’s not possible to tell the difference between say 95% illumination and 100% illumination so depending on how good your eyes are a full moon can appear to last for typically around 3 to 5 nights. read more