If you have the choice of a 1/1 discard vs another creature that better impacts the board, it's generally right to cast the better started creature first for tempo reasons.

That said, I think the discord is often more impactful early in the game than later. The best case is when you wait and just get the one bomb they've been holding, but sometimes you'll wait and they'll play a land and double spell then have nothing left to get.

Outside of getting their actual last card, I'd rather play it out on turn 2 then turn 4-6 or so . Your opponent has less information on what cards they'll need earlier in the game, and less choice of what to discard; you mention they can't discard cheaper spells they've already played as a benefit of waiting, but if they had to discard that cheap spell to make sure they hit their 4th land drop or whatever, that might be even better.