In an update on Daniel Bryan capturing the WWE Championship from A.J. Styles this week on SmackDown Live, Dave Meltzer of The Wrestling Observer Newsletter gave more details on when exactly the decision was made:

“Daniel Bryan has been pushing the idea of going heel.

“Whatever the reason, I don’t know the reason. But it was over the weekend, Vince changed plans and wanted to go with Brock Lesnar against Daniel Bryan. This is before the Becky Lynch injury. The heel turn was decided [Tuesday] afternoon. It was basically Vince saying, ‘Let’s do it all in one day and get the biggest impact.’ 

“But this was not scheduled for Crown Jewel, nor anywhere until the weekend. The heel turn was talked about, but not decided if or when until the afternoon of the show, where Vince made to call that if they are changing the title, they may as well do it all at once for maximum shock value.”

PWPix.net also reports that one of the reasons why the title change occurred was because Vince McMahon did not want A.J. Styles to suffer a second loss to Brock Lesnar at Survivor Series, but he also felt that having Styles go over on Lesnar was not an option either. The feeling is that Daniel Bryan will be able to work well with Lesnar and have a good match with him, and Bryan is also scheduled to have a considerable push as a heel heading into WrestleMania 35.