Twice Upon a Time

In every zone other than the stack, Twice Upon a Time uses only its non-Adventure characteristics, and you ignore its alternative characteristics in those cases. For example, while it's in your graveyard, its mana value is 6.

If an effect copies an Adventure spell, that copy is exiled as it resolves. It ceases to exist as a state-based action; it's not possible to cast the copy from exile.

You must still follow any relevant timing rules for the non-Adventure spell you cast from exile. Normally, you'll be able to cast it only during your main phase while the stack is empty.