How soon do you have to send a thank you card?

How long do you have to send a thank you card to someone for attending your baby shower, wedding, or another gathering? How about if they sent you a gift for a holiday? I read that you are supposed to send a card within a month, but that seems impossible. I thought maybe a year, but my mother-in-law...

Do you prepare talking points before a gathering or just go with the flow? Why?

I am wondering how to be a better conversationalist at gatherings....