With a split like push/pull/legs, you have no carryover in body parts. So in that example (not that you cannot train on another split), you can train every other day and hit each body part once every 6 days.
Dorian Yates states that in the sense of progressive overload. Meaning, the idiots that go to the gym and never ever use heavier weights aren't forcing their bodies to adapt. He doesn't mean you can barely inflict any damage on a muscle, wait 2 weeks and come back stonger AND bigger. Granted, I know he was Mr. O and chemically enhanced, but notice any difference between his volume and a mentzer routine? Yeah, like not even on the same wave length comparable. Go to bodybuilidng dot coms site and check out the DY trainer series. He shows you exactly what he recommends. It is nothing like a mike mentzer plan.
Again, HIT works, Mentzer does not. I am HELPING you not waste time on his routines like I did. I promise you will do better on a Yates/MAX-OT/other low volume program.