It doesn't matter if the area is explored or not or if the target is inside the fog of war or not or how far away the units are. If there is another unit on a tile you have sent a unit for just one turn (visible or not) your unit will just stop and you have to give them the same orders over and over again, if you still remember where you had originally sent the unit.
I think the units should just go as far as they possibly can and not stop if somebody blocks the hex around 30 turns before they actually get there.
I think the units should just go as far as they possibly can and not stop if somebody blocks the hex around 30 turns before they actually get there.