It appears that the crux of the doctrinal change the Jackson was making is the signal of the start of the Great Tribulation.
Prior to this meeting their teaching was detailed in the July 2013 Watchtower which says
“In the larger fulfillment, the “standing” will occur when the United Nations (the modern-day “disgusting thing”) attacks Christendom (which is holy in the eyes of nominal Christians) and the rest of Babylon the Great. The same attack is described at Revelation 17:16-18. That event will be the beginning of the great tribulation.”
Jackson now says the start of the GT is when Nations suddenly hand over their political power to the United Nations. From the OP transcription, Jackson said
” But don't expect you will see Governments wanting to gradually give over power. They don't want to do that. It takes an act of God. Jehovah will put it into their hearts. This will occur with suddenness. Yes, then the GT will start.”
Their idea is that the attack on false religion will follow.
It may be that the reason for this very minor adjustment now enables them to call the start of the Great Tribulation any time they like since -
Nations have and are signing over certain powers to the UN already. For instance, agreements made and being negotiated with WHO.
The chances of the UN destroying all religions except the JWs doesn’t appear likely or provable any time soon.