Potty training, when to switch to the toilet

When is the right time for my son to switch over to using the toilet? He is already very proficient in using the potty chair

Let your son decide for himself. If he shows an interest in the toilet, then by all means help him achieve his goal. If he shows no interest then you might casually suggest that you will help him with the grown-up toilet whenever he is ready. Of course, when you are out and about you have no choice.

I suggest then that, for hygienic purposes, your child squats over the toilet opening, rather than sitting on the seat, with his feet on the porcelain bowl, and you holding him.