THe GM service manual I have cleverly says:
"adjust timing to underhood label specifications".....
....the only numerical reference I find is "when the ECM test advances the spark to 20°, the knock sensor must set a DTC"....implying timing is less than 20°....
...that is rather minimal info......
check thisd out...
http://www.autozone.com/az/cds/en_us...rInfoPages.htm