Individual installations can last anywhere from 8-12 weeks, given the care provided and what kind of hair you have.
Factors such as the sebum production rate of your scalp and the rate of growth for your own hair will cause a shorter installation period.
With proper care, the extensions can be reused for up to 3 reinstallations or a little under a full year of wear. Some clients CAN use their extensions for a full year or longer - it all depends on what activities and preventative measures are used.