So what exactly makes operational surprise in any prospective armed reunification actions impossible? In the time it takes US or Taiwanese observers to confirm that the PLA is massing, the PHL-16s and TELs would have already driven to their positions and fired. Distributing your assets also takes time. You're not getting your airforce into hardened shelters or dispersing enough with <1 hour of notice.
There could be weeks of warning that China cannot hide in the face of visible events to be observed by the US and allies.
, so let's consider aircraft sorties near Taiwan. When the invasion begins, China will require aircraft of all types, ready for immediate combat from the start of operations. All complex military equipment is not regularly maintained at this level of readiness, so there will be an increase in the number of aircraft being previously maintained. Much of this will be minor and preventative, for example, say a part must be replaced after 8,000 flight hours, but the PLA needs to replace while the aircraft's flight hours have not exceeded more than 3,000 hours. All of this will be scaled up and coordinated by the PLA, so the pace of pre-operation maintenance will be large enough to not be visible.
This will be particularly obvious in satellite space assets as more aircraft are on the ground with ongoing maintenance, either in the open or under cover. Missions towards Taiwan may continue at a high pace, but the composition will change to older aircraft that will have to fulfill second-line roles once the war begins.
This will also be repeated for land and naval assets. For warships, one can expect several short refit periods (3-12 weeks) outside the standard and very predictable refit cycle with the longer periods boasting obvious visible covers. For example, if a ship typically undergoes a minor overhaul in the spring of even-numbered years (based on certain US patterns I've seen in open source data) and starts one in an odd-numbered year, something unusual is happening, and when several rupture the SAME cycle, war is imminent. I could expect at least three weeks' definitive notice. Longer alert times are possible with enough intelligence and good analysts.