I feel (a little bit) differently about the "thank you" cards as the above posters.
I do not pre-write them, because I write a different letter to the admission staff and a different to the clinical rotation or financial aid or the person who interviewed me or the dean.
I just write something like I would like to express my gratitude ..... etc
I wrote a Thank you note to every single person I met and helped me to know more about the school, etc...
I also send it the same day, so they get them when they still remember me.
HOWEVER, I do not write anything about "I would like to attend the school, or be honored to attend school, etc.
I feel the Thank you cards should be Thank you cards, not another way to "sell myself". They already know I want to get accepted, otherwise I would not go to the interview.
That's just me, but I feel it is inappropriate for me to write about attending the university, because I do not want them to think I wrote that letter to get acceptance, I want them to know I thank them for the opportunity to go and see the school, interview there, meet them, etc...
I know the thank you cards do not play a role to get acceptance, but I feel when you write about "i want to attend" it's losing the original purpose of the Thank you card. They already know you want to go to that school. "I want to attend" letters are the letter of interest/intent letters. You can write LOI if you want.
I do not think, there is a good or bad way to write letter, they all good.
I do not want to start an argument about this, that's how I feel about it and just wrote this post, so you can consider another viewpoint. That's it!
So, to answer your questions:
1. Same day or next day.
2. You can thank them for their time to interview you, read over your file, the info they provided, for the tour,etc.
Whatever your experienced was in the particular school you went.