Looking at things, it will most likely be a full campaign. This is because the time it takes to complete a campaign in normal is usually below that period (1 hour) I believe that if both teams are skilled, the game will actually finish faster (probably within 45 minutes) simply because both teams know how to score. (If its too fast, it defeats the purpose)
Generally the auto-score recording mechanism makes things easy to handle, which reduces the down time usually.
Even if they are halted by the infected, it could simply mean they're taking their time to heal up or pick up ammo. Take it as an expert mode campaign time frame. Usually between 1-1.5 hours.
As for the Auto-director in L4D can be disabled and replaced by configs, but that way, most of the spawns and numbers will be the same. The auto-director tends to favor the losing team with spawns (tank particularly) but by removing that, you may lose the suprise factor of the game.
Generally speaking, L4D isn't made for professional gaming, more towards semi-casual to semi-competitive plays.
We want to make it fun, challenging and let people get something out of it in the end

E-club is hosting the time challenge, ESPGL will still host the VS compy in march. So don't worry. Join the E-club one, have some fun (you might see us there too) and we'll see you again in March for the VS compy!