They were available to anyone on the qualifying realms, but Blizzard adjusted it so that if you were in queue to log on, you could also access the shop from the queue window. That way people wouldn’t be stuck waiting for hours just to initiate the transfer once they could finally log in.
There was a sticky at the top of the forum that said the transfers were open from Wed-Mon of this past week.
The announcement also made note that if enough people transferred before the deadline they would close the transfers early, with no notice ahead of time.