This came up when a sorcerer cast chromatic orb in my campaign. It was only after hitting and rolling damage that the sorcerer decided he wanted to twin the chromatic orb, and I ruled that he should have declared he was twinning the spell when he cast the spell, and not after knowing the results.
He was frustrated when he read the description of twinned spell and didn't see that explicitly stated.
At what point in casting a spell would twinning the spell still be possible?
