@KatherinWinterThey're like 4 times as fast as normal dogs, able to walk up walls and deform to slip through cracks and stuff like that, with a dog sense of smell, hearing, and keen ability to detect the supernatural. If you mean how far they can physically get from Curwen, as far as they like.
The Case of Charles Dexter Ward ended with a shade being called up essentially by accident and then going halfway round the world of its own accord to put down the rest of the antagonists.