But they won't be aware until the final moments unless you tell them. I can provide with two things:
(A) The means to let everyone know they have 36 hours left. You can only tell everyone; no selectively picking who to inform
(B) Legitimacy so that no one dismisses your words as a hoax, insanity, etc. If you tell them, they will react with the full knowledge that the world is ending.
I have other stuff to do with my last hours so you have to decide now.
Shall you tell them?