[mwebb]

i do not understand your question , then again
you do not have a question

your statement is false do not proceed with your experiment .

the answer is
AVERAGE
peak combustion pressure must happen at about 14 degrees after top dead center

not so important at idle as at every other condition of engine operation
spark duration is almost always longer than 1ms but the combustion event itself takes much more time than the time for the spark event
the spark event will end before the combustion event

the timing advance / change for the spark event
changes
with rpm and load and temperature
and
the spark event is timed so that the combustion event produces peak pressure at 14 degree after TDC
=================
if
peak combustion pressure does not happen at 14 degrees after TDC because someone tampers with base ignition timing
peak power and peak efficiency are reduced / decreased
emissions increase
and
if base ignition timing is advanced enough so that some random combustion events get to peak combustion pressure before TDC
the engine will be damaged .

do not frack with it