How long ago WWE decided on The Rock vs Roman Reigns for WrestleMania 40

Even though Cody Rhodes won the 2024 Royal Rumble match, it doesn’t look like he’ll be finishing the story at WrestleMania 40.
Rhodes appeared on the February 2 edition of SmackDown to announce that he won’t be challenging for Roman Reigns’ WWE Undisputed Universal Championship in April, before The Rock made his entrance to confront the Tribal Chief.
Per Dave Meltzer on Wrestling Observer Radio, The Rock wrestling Roman Reigns was included in The Rock’s deal to join the TKO Board of Directors.

Indicating that plans for The Rock vs Roman Reigns have existed since January 3, Meltzer said:
“When he made the deal on January 3 to come in, that was part of the deal.
“Why Cody Rhodes won the Royal Rumble is a question that I cannot answer because nobody will answer it for me.

“But, the belief was that it was Roman Reigns and Cody Rhodes, and nobody knew, but the deal had been made prior to that.
“It played out the way they wanted it to play out.
“The plan as of Friday night was Seth Rollins and Cody Rhodes.”

The Rock notably teased a bout against Roman Reigns on the January 1 edition of Raw days before this deal, hinting that he wants to sit at the head of the table following his altercation with Jinder Mahal.
While the match hasn’t yet been announced, it was reported that “numerous WWE sources” expect The Rock vs Roman Reigns to be officially announced for WrestleMania 40 during Thursday’s (February 8) WrestleMania Kickoff event in Las Vegas.