Christmas might not be bad for soft openingsI think it will be open for Howl-O-Scream, Christmas the latest. Both Halloween and Christmas are big money makers for BGT-- opening Iron Gwazi would be a draw for one or both of those as well as something to keep locals coming all winter in what would be a deadly slow (slower than normal) time of year. Year round parks really don't have to launch a ride in spring.
Labor Day would be greatNational Roller Coaster Day is August 16th, though a Sunday grand opening would be a bit unusual - but maybe they could spin it as National Roller Coaster Weekend and open it on Friday or something - although that's only like 12 days away so it might be a bit too ambitious.
Labor Day weekend would be my next guess.