I was able book a trip from YUL to LAS for next weekend so the deal was still active at 11:00 PM EST
I just tried to book a trip to NYC and got the dreaded "this voucher has already been used" and then after hitting apply/reprice a few times it worked. But when I changed the credit card from Amex to MC it changed SAVE300 to ENTERREDEMPTIONCODE in the voucher code box and wouldn't work. Very weird