Left 4 Dead 2 Gametype announced

On Planet Xbox 360, Valve announced a new gametype in Left 4 Dead 2 titled Scavenge:

Scavenge mode challenges players to compete in round-based games of up to 8 players (Survivors vs. Infected). The Survivors must battle both the Infected and the clock as they collect gas cans to refuel a generator located in each map. Every can the Survivors pour into the generator scores their team a point and adds time to the clock.

So it's basically survival with a continuous attempt to fuel a generator in order to put more time on the clock, okay not a bad idea. I'll have to see how it plays, but if there is a timer, what happens when that runs out? Does the timer represent a moment of respite for players, so that when the timer runs out horde's start coming?

That would make sense, the hordes are so bad you HAVE to keep filling the generator so all you have to face is the enemy team of special infected. Thing is, that's probably a bad guess being I can't see the game type letting you avoid hordes just by adding to the clock. So what happens when the timer runs out? The round's over? Also doubt that, because it's kinda lame to see the round end when the timer runs out. Does the timer replace simply dying like in survival, letting you respawn to help your friends. I also doubt that because it would be redundant to respawn in a zombie survival game. But what significance does the clock running out have that overshadows the struggle to stay alive against the infected?

Edit: All questions answered in this video