As the headlines from ESA's website had it: PLANCK REVEALS FIRST STARS WERE BORN LATE
There is a revision from the current estimates of 500 million years by an additional 50 million years after the big bang. This put the birth of the first stars at 550 million years after the big bang. The details of how the measurement is done is also explained in the link above. The age of darkness as revised by PLANCK's high resolution data now starts from 380 thousand years to 550 million years after the big bank.