The war over Taiwan wouldn't be done by soldiers on Taiwanese soil. So you wouldn't need many boots on the ground in a literal sense.

But if you mean in a metaphorical sense, how long until the 7th Fleet could get to Taiwan, the answer is 0 days for first response, 3 days for everything located in Japan, and less than a week for the full mobilization of the 7th Fleet (that's 50+ ships and nearly 30K soldiers). The entire Pacific fleet could be there in a week and a half.

(Granted, we're assuming competent US leadership, which is not the current administration.)