Timing is manually set. The ECU assumes it's set to 3*. The ECU can (and will) retard down to 0* so setting it too high can actually be detrimental.
I wouldn't go higher than 5* if running regular and 7* if running premium.
The ECU actually does a pretty good job of advancing the timing when running higher octane fuels, which is why such little timing advancement is needed. If you run 7-9* on regular, you will find the ECU retarding the timing to 0* (which is actually 4-6* as you've advanced it mechanically) when you get on the throttle which is bad.
I wouldn't go higher than 5* if running regular and 7* if running premium.
The ECU actually does a pretty good job of advancing the timing when running higher octane fuels, which is why such little timing advancement is needed. If you run 7-9* on regular, you will find the ECU retarding the timing to 0* (which is actually 4-6* as you've advanced it mechanically) when you get on the throttle which is bad.