ChadGadya, only RSZA ztl talks of midnight but lechol hadeyot, midday and midnight are ALWAYS 12 standard hours apart.
to all: we announce the “average lunation/ molad” the actual molad varies by as much as 9 hours, i believe, given the elliptical orbit of the earth around the sun. chazal’s estimate of the average lunation was correct to 5 decimal places. the accumulated error over 1500 years is about three hours in the right direction, making the bias in RC later. in about 5000 years a sanhedrin will have to correct deleting one 13th month and one 30th day. nothing to lose sleep over. both the 19 year cycle and the average lunation are approximations, the lunation a remarkably good one, the 19 year cycle a bit less so.