I'm pretty sure it depends on the program. Some programs most likely don't care as they don't look at applications until everything is sent in. Other programs look at applications as a first come first serve thing, so the earlier the better. Only one of the programs I applied to even mentioned when they start looking at applications (earlier = better).
Someone should correct me if I'm wrong, but I think for the majority of programs it shouldn't matter, as long as it gets there.