When experimenting with it, it appears to work in that a 4 note chord gives the normal timing... aka 4 notes gives the same results with or without whiplash on. If playing fewer than 4 notes, the arp slows down to the equivalent time of a 4 note arp normally, and more than 4 notes speeds up the arp to still fit within the 4 note normal arp timing.
So, 4 notes is the standard timing. 2 notes would be half the speed, 8 would be double the speed.