It's possible to hear a little earlier. Looking back on past threads ('cause I clearly don't want to be studying right now, haha), Class of 2016 was told they'd hear by 12/22 and ended up receiving interview invites on 12/20. Class of 2017 was told by 12/21 and though a few were able to check the interview portal on 12/20, e-mails were sent 12/21. Our class was told 12/20 and we received e-mails on 12/20.
I'd just assume 12/19, since they've been on time the last two cycles. It's not that far away, though it may seem like time is dragging on!