I seem to remember that there used to be such a rule when I first started instructing, but that was over thirteen years ago.
I know that as an "AFI" I had to build up 5 hours on a Grumman Cheetah before I was allowed to instruct on it.
I've just had a brief flick through "Lasors" and can't see any mention of a requirement to have 5 hours on type.
It sounds to me like you've been talking to somebody who hasn't kept up to speed with current legislation.