With rotary processing I always pre-soak for five minutes in tap water. Pre-soaking is very important with this method of development when using staining developers like PMK, Pyrocat-HD and Rollo Pyro.
Tests have show that films react differently to different time pre-soaks. My understanding is that the five-minute time is based on the fact that nearly all films reach a similar equilibrium at about five minutes of pre-soak. This would presumbably be based on the fact that by five minutes the gelatin will have absorbed all of the water it can absorb.
As for the Ilford and Agfa advice that pre-soaking film lessens acutance I think that is just pure nonsense. I seriously doubt anyone could devise a test that would show this to be true with normal processing of film.