Sorry, I see your point now! Technically, you could represent all data as a 6-dimensional vector, where A-F have zeros at the 6th dimension and 1-3 have zeros at positions 1-5. But, yeah, that’s probably too far fetched :).
Then you probably can still try to treat your problem like a sequence-to-sequence task. While 6 many-to-one network will work in principle, you obviously use the dependencies between the outputs – I assume that the 6h output not only depends on the input but also on the outputs for hours 1-5.