Future Perfect Progressive

Form = will have been VERB+ing

By the time Max shows up to work, Mary will have been working for more than two hours.
By the time Sam graduates from Harvard, he will have been studying there for more than twelve years.

The future perfect progressive is used to emphasize the continuous nature of an activity or event over a period of time and up to a particular point in the future. This sense of the future perfect progressive is usually expressed with a time expression of duration. The point in time that the activity or event starts may be before now or it may be in the future.