2.Your appointment is _______ (at,to on) Saturday.

on为什么不选at老外就是这么用的，星期前面都是用on，可以帮你搜一点鲜活的例子，请看下面这个帖子：Psychiatrist appointment on Monday, help?Hi, I see my psych once every month and my next appointment is on Monday. I have been having an awful time with depression, disturbed sleeping pattern, not leaving bed, washing etc. I feel so awful. So I decided I would get high (legally) with OTC meds. They made me mildly hallucinate and made me feel nice, calm and happy. I loved it so I did it again and again. Each time crashing down harder than before. I am scared it will turn into an addiction. Feeling nice, calm and happy but crashing down harder making me want even more. Shall I tell my psychiatrist this? What will he say/do? I just feel awful