The timing will retard a bit from cam belt stretch and the normal minute wear of the cam distributor mating.
Not a lot, but in that direction over time.
Advancing the ignition timing gives you all the power and economy that is in the engine. Spark knock is the limiting factor.
Pick the fuel you want to use, and adjust it accordingly. If you hear a rattle here and there, retard it a couple of degrees.
But like mentioned, the sticker should be under the hood, for stock settings.