With an `On Demand Hydrogen Unit` is there any advantage in advancing or retiring the ignition timing?

Hi yes mechanically there would be.

Retarding.

I assume you are talking about a hydrogen generator or "Brown's gas" system that generates hydrogen from water, used to supposedly cut down on fuel costs.

It's all a scam, it is impossible to gain any advantage, as more power is used generating the hydrogen than what burning it gives out! This guy Brown was a person who was running gas engines purely from burning hydrogen and oxygen generated from water. His great claim to fame was he was mixing the hydrogen and oxygen components together supposedly safely, but had absolutely NOTHING to do with low costs!

If this is what you have, forget it. It is an impossible system.