The walking corpses are about 20 feet away, the archers about twice that. I figure that to turn undead, you have to be pretty close (about 10' or so) so it makes sense for Aldbane to advance towards the corpses and attempt to turn
Aldbane will stick to his original plan of waiting for a round of missile fire before going in to melee. But if the other party members forego missiles, he will wade into melee now.