Rel
Liquid Awesome
Here's a rusty-to-the-point-of-being-a-newbie-GM question; if the game is going to be about six hours long, how many assassinations should I plan for? It seems like maybe three would suit. Or possibly more if I threw in Rel's suggestion of having to hit two simultaneously. But right now I'd be blindly guessing an estimate. (And maybe I should caveat that the gaming groups that I'd run this for are friends, so I'd be given more leeway for imperfection than say at a Con with strangers.)
I'd say two or three. Remember, you can always throw more complications in their way as you go.
But my bigger concern is that I've never seen a Dread game go six hours and that seems like it could be a problem. Consider that the only method of conflict resolution is pulling from the tower. Even if you move at a very slow pace, your tower should be getting VERY unstable by 2 hours into the game. Assuming that somebody knocks the tower over around that time then they are effectively out of the game for the next four hours. Even if they aren't killed and they are Dead Man Walking, they can't make any pulls for the rest of a four hour session.
I'd be wary of dragging things out too long with Dread.