Form
Subject + will + have + been + Verb-ing
The man will have been walking the dog for an hour by noon.
We will have been eating dinner for an hour by then.
Meaning
Duration Up To a Future Point
Used for an action that started before a point in the future and will continue up to that future point. It emphasizes ‘how long’ the action will have been happening before the future reference time.
PastPresentFuture
x
By next year, I will have been working here for five years.
At 6 PM, she will have been studying for three hours.