Reading thru this slowly, we can see how the 25A cannot be used for a political coup.
The VP, in concert with the Cabinet Secretaries, can deliver to Congress a declaration that POTUS is unable to perform.
VP becomes \acting\ POTUS.
Within that very same hour, POTUS can deliver a declaration of competence to Congress and resume position as POTUS.
No buts about it.
Again, I will point out that an acting POTUS is NOT CinC and therefore, Military Command Control transfers immediately to the Military Officers as assigned by POTUS and outlined in the Change of Command Control Plan...Devolution.