Употребляется для описания будущего действия, которое совершится до определённого момента в будущем

может быть выражен:
конкретным временем
by 5 o’clock
by tomorrow
другим действием в будущем
before they go home,
by the time you ring me up

will
have
V
ed
3
Future Perfect: образование

Future Perfect:
Negative Form
not
The play
will have begun
-
-
not
will
have
V
ed
3
7 o'clock.
by

Future Perfect: Interrogative Form
have
V
ed
3
S
will
General Question
Will
the play
have begun
by
7 o'clock
?

Future Perfect: Interrogative Form
Special Question
Wh
S
will
have
V
ed
3
By what time will the play have begun?
Why will the play have begun by 7 o'clock?