General info:
2018-2019 Survey Schedule:
http://www.arbitron.com/downloads/Survey_Schedule.pdf
Nielsen Audio PPM Release Schedule (displays the next three survey periods; gets updated once a month):
https://www.rrconline.org/arbitron/schedules/ppmSchedule.php
Nielsen Audio Data Delivery Schedule (use drop-down menu to select market name and survey period):
http://www.arbitron.com/home/delivsched.asp
Thus, the Holiday 2018 results should appear at 5 PM ET on Tuesday 1/22/2019 (delayed one day from usual due to the Rev. Dr. Martin Luther King, Jr. holiday).
David was referring earlier to the re-release (during the last week of December) of the December 2018 survey.