For quenching, it is the cooling rate that determines hardness. Basically the amount of heat in the bullet, conductivity of the material and change in temp. Yes there is steam created when quenching which does reduce the rate but nothing we can do about that with H2O. The alloy doesn't have enough 'other' stuff in it to affect the process but of course the result BHN will be affected. Reverse the process for heating. PC baking gets the bullet up to temp in ~15 min. Then you have to add time for the molecular mobility which appears to be ~ 1 hr for 'normal' weight bullets. If casting those really big ones, I'd add some time.
BHN readings for high BHN are not too accurate due to 'spring back' of high Sb alloys. Additionally, the smaller 'crater' leaves a higher uncertainty in the measurement.
I've been PC cooking on a hot plate as I stand them up, just easier. Temp control is more difficult and the target shows it (HV rifle) so I now re-cook in the oven. WD for both processes. Easy and can't hurt.