Yep, the only reason I say they'll more likely just threaten him with it to make him "voluntarily" step down is that his followers would rebel against Vance if he outright power ousts him with the 25th.
But I think he (actually they, the whole cadre that are running things) will go ahead and actually invoke it if trump refuses to cooperate. It'll just take more work--either a propaganda effort of video clips, rumors, leaks of "doctor reports" and "off-camera incidents", etc. to convince his cult that he really is unable to continue, or more likely something might just "unfortunately happen" to him. They just have to make sure the magats don't smell a rat and turn on them.
Oh, and the reason to wait until beginning of next year is so Vance will be able to run for two more full terms.
No problem, he just applied for a job with ICE and was hired on the spot.
/s