The pace that we expect players to play at does not depend on the state of the game/match. If a player in a Modern event is comboing off in game 3 with 20 minutes left on the clock, and has resolved a
Pact of Negation with no way to pay for it next upkeep, then, barring extremely unusual circumstances such as a double Game Loss, the match will be over by the time the active player's turn comes around again. Nonetheless, we expect the player to continue play at a reasonable pace; he doesn't get to “stretch out” the remaining turn. Similarly, it's not an issue if a player has been playing at a reasonable pace and, as time approaches, she continues to play at this pace in order to ensure that her plays are thought out. While some players will play faster in hopes of concluding the game, it's not a requirement.
We consider the players waiting to come up with their match result part of the match, because we also need this to conclude in a timely fashion. The players can't wait 10 minutes to give a match result, because that violates the pace of play. The players can't argue that they aren't holding up the tournament: imagine if two matches were both trying to wait on each other to give a result! If push comes to shove, you can definitely apply the rule that Nathan cited, but I'd only do this in a very extreme circumstance, although if the players are refusing to provide a result when you instruct them to, you have a bigger problem on hand.
As for stalling, this is not Stalling because that specifically requires taking advantage of the time limit. The time limit isn't the issue here, so it's (thankfully) not a DQ offense.