I disagree, if you give the humans time to disperse and fortify themselves, it would be very difficult for the zombie to convert others. Additionaly, since it is a random person, regardless of how much time you allow before the zombie is spawned, you will always run the risk of having it spawn right next to you or your group. Except you will have no chance at all if you have already fortified yourself in with the zombie heh .
Shaftiel
Okay, but It need to be at least a little longer. On the level City Defence (i think it was) the T's spawned in a room with a slow opening door.... If it you spawned in there then they were all Zomb's no matter what.