Suppose you send a message to a person which is not online!
By the time you see this message I will have been done with my task
means that my task is already finished some time before he or she sees the message.
I want to know what is the difference in meaning if I change the second clause to a present perfect:
By the time you see this message I have been done with my task.
Is it grammatical at the first place? This question comes just from my curiosity.