How long can a planetary nebula remain visible before merging into interstellar gas?

A planetary nebula typically remains visible for up to approximately 30,000 years after the ejection of its gas shell.1

During this relatively brief period, the nebula expands outward from its central star at speeds typically ranging from 24 to 56 km (15 to 35 miles) per second. As the nebula expands, its density decreases, eventually reaching a point where the gas becomes too tenuous to be distinguished from the surrounding interstellar gas, at which point it effectively disappears. This lifespan is considered short when compared to the total lifetime of the parent star.231