Latency: the time period between the ignition event and the formation of a flame front.
This is why differing fuels will have differing EGTs and CHTs when used in the same engine. The G100UL has a latency very, very close to 100LL so there will be no need to change the timing on the engines. It is a drop-in replacement for 100LL and can be mixed with 100LL during a transition to unleaded fuel. And, it requires no special handling as 100LL does.
Knowing the latency of the fuel is important in the calculation of where the ignition event is engineered so as to produce the peak combustion pressure at about 15-16dAFTDC where the con rod-crank geometry transfers the most mechanical power from the chemical reaction inside the combustion chamber to the crankshaft.