You will only get a gain if the timing is not already optimised.
Hard to give an exact number of timing to use because it depends on several variables. The cheapest way to do it is advance it, test, check for pinging, advance, etc until it pings
If you are not sure what pinging is, then ask a mechanic or a knowledgeable mate to point it out and explain the mechanics of fuel quality on fuel burn and ignition advance. I think detonation/pinging is best explained with a real life example.
Too much timing (regardless of the fuel) can be bad and damage the engine.
That should get you started.. come back with more questions