Yes, the GAC change date has been pushed back, according to someone I talked to in City Hall.
I am not sure a GAC could really do much - even the wheelchair accessible queues are in direct sunlight more often than the regular queues.
DL has different GAC stamps than WDW, and I am not sure if there is one for the sun.
My best suggestion would be to talk to people at City Hall anyway, just in case, but also to make plans just in case they cannot help you. Go see shows and indoor things during the heat of the day. Save rides for early morning or after dark.