Online Magic is not the same game as paper magic, and in online magic, your match clock is a resource just the same as your life total or cards in hand. I don't believe there's any etiquette requirement to scoop a game of MTGO under any circumstance, nor any shame in drawing out a lost position when your opponent's clock is in the red zone (after all, perhaps they're winning because they spent a far larger amount of time than you in the tank optimizing their play earlier in the match?)
However, I will concede games as a courtesy in certain situations:
- overwhelmingly lost positions in game 3 when the opponent still has copious time remaining on their clock
- when the opponent has played a lethal Tendrils and just needs to click "same target" a billion times
- when the opponent is comboing off and (a) I'm confident I have no interaction or counterplay, (b) the opponent is playing quickly and it does not appear clock time will be relevant in the matchup, (c) I'm already familiar with the full contents of the opposing deck, and (d) there is no chance of the opponent fizzling, losing to their own Mana Crypt, etc.
Certain circumstances nearly guarantee I will force the opponent to play the game out:
- they have been whiny or salty in the game chat
- they have been showboating with storm count or Mentor triggers instead of finishing games quickly.