Future Perfect Continuous

Future perfect progressive is a verb tense that you might never use; it’s
pretty rare and almost never necessary.

Future perfect progressive has almost exactly the same meaning as past
perfect progressive; the difference is that it happens in the future, not the past.
We use future perfect progressive when we want to make it clear that the
action will happen
*over time
*until (or almost until) something
* in the future.
That’s one reason we don’t use this tense very much; it doesn’t happen
often that we need to say that something will happen over time until something in
future. Another reason is that we can usually use other tenses instead of future
perfect progressive.

Statements:
will have been + verb-ing

Examples:
I hope that when I get home tonight, my son will have been doing his
homework.
When June gets home, Ward will have been grilling the burgers for about
10 minutes.
John’s shift at work starts at 8:00 tonight, but Marsha’s starts at 6:00. That
means that Marsha will have already been working a couple of hours
before John arrives