The when is as varied as the one proposing the timing. The Who is set in stone.
Abraham knew when Sodom would be destroyed, Lot did too. But everyone else didn't.
Noah knew when to enter the ark, the rest of his family as well, but everyone else didn't.
Elijah and the prophets knew the day he would be taken up, but likely they were the only ones and only Elisha refused to leave him.
Jonah proposed the timing of 40 days. That was from God, He relented because they repented and didn't know the right hand from the left.
God says He doesn't do anything without first telling His prophets. No doubt that would include the rapture.
God also said He tells us the end from the beginning because it is proof that He is God and there is no other. Again, that would certainly apply to the rapture.