Ronvid currently triggers from graveyard at end of turn. There are other end of turn triggers such as the Knight Elect buff
Regarding timing. If your opponent has already passed, as soon as you pass the round immediately ends - no end of round trigger occurs. So you can't use Ronvid as turn 2 carryover after opponent drypasses.
If opponent hasn't passed and you pass, Ronvid triggers as the turn has to end to move back to opponent.