I live in Canada.
In 2014 I booked our fall 2014 stay at about 0100 on 05-07-2014. The free dining offer link was not shown in the "special offers" dropdown list on the WDW website, but you could go directly to the link and book. USA people had to wait a few hours. As of 3:26 that morning only the Canadian offer was available - people coming to the link from a USA IP address/with a USA billing address got a message that the offer was only for Canadians. By probably about 8 am or maybe a bit later the USA offer was up.
The late fall 2014 room only offer dropped July 23 at about 7 am; we booked it at ~0720 by phone (we were changing a reservation from
AAA to RO discount) and were the first RO offer reservation the CM had dealt with that morning.
In 2015, both USA and Canada as well as Free Dining and Room Only offers for late fall 2015 came up at the same time. 04-27-2015. I had booked online by about 0600.
SW