Simultaneous purging of the chief generals of all three branches.
They are ensuring the military has no cohesiveness to stage a future coup against the Executive Branch, and are replacing all control with their own loyalists.
One absolutely doesn’t prepare such a large operation at such a short notice.
For an intelligence analyst, signs of an invasion are typically detectable 3 months ahead. If one performs a maritime invasion at a notice of weeks, failure is likely. (For reference, the D-Day needed years of planning and months of moving resources to work.)
Also, I trust that Taiwan has infiltrated China just as deeply as China has infiltrated Taiwan - they likely cannot keep massive secrets from each other.
You assume they haven’t already been planning for months, or years.
