That variability in time to transition FD modes results from the AGL at which you pressed the TO/GA button. If you press the TO/GA button at LPV approach minimums, it is going to sequence flight director modes as soon as a positive rate of climb is achieved. If you press the TO/GA button just prior to actually reaching the runway (very low AGL), the system holds wings level (GA lateral mode) until you have both achieved a positive rate of climb, and flown away from the ground to a reasonable threshold.
I think you will find that pressing the TO/GA button at LPV approach minimums will lead to a very quick transition of flight director modes. If you are in a situation you are pressing the TO/GA button beyond approach minimums, the system will hold you wings level for a bit longer, before it begins any kind of lateral GPS course correction, even if it is very slight.
Thanks,
Justin