There are no elements of surprise when it comes to attacking Taiwan (at least when it comes to unification). Massive of troops will be detected in advance. Only a few beaches where Chinese troops can land, and they are all fortified. Only a few months of the year where amphibious style crossing is possible.
It need not have to be so.
Campign will start with sea and air. Nullify of median line means zero early warning for Taiwanese air defence. PLA can afford to attack with no warning.
Most of the land equipments like tanks, artillery, signal equipments etc needed for ground campaign would already put in storage in various locations in Fujian and Zhejiang.
What needed is the mobilisation of troops to operate them. With HSR network, large number of troops and light equipments can be mobilised to fujian quickly. I dare say PLA ability to mobilise manpower and resources is unmatched.
With this arrangement, China don't need to maintain large number of ground troops in Fujian.
Mobilisation can start right after commencement of air and sea campaign which my guesstimate will take 4 to 7 days. This period will be enough to gain air and sea control as well as Penghu. Thereafter ground campign can begin.