There is actual research on these questions. You could read about the transition and see that according to places like Cleveland Clinic or Mayo Clinic, it takes 18-24 on average to transition fully from man to woman. The hormone therapy actually includes anti androgen as the first step, which blocks testosterone and it’s effects on the body. One of the first effects seen is loss of muscle mass. Unlike estrogen, testosterone is a fast acting short half life hormone and the effects of blocking it will be seen relatively quickly, within a month. Estrogen on the other hand is slower acting and longer lasting so much of the 18-24 month period is about developing woman characteristics, not losing male characteristics. Anyway the short answer to your fist set of questions is, two years after you start the transition from man to woman the process is complete.
As to your second set of questions, how about considering the reverse. What if you were the parent of a trans kid that wanted to compete in swimming? Your child had gone through a physically and emotionally exhausting 2-years long medical procedure and then they started training daily to, getting up at 4am, etc., to peruse their love of swimming only to find that people want to exclude your kid from the team and competition. How would you feel? You can appeal to emotional heart strings on both sides of this issue.