Coffee Chat Follow up advice

I got in touch with the director within a BB bank. I had about a 40 minute call with him. Asked some questions and genuinely had a nice convo where I learned a bit about what to focus on in school, his career, and some nuanced things about what happens in his line of business. We agreed to stay in touch and he even is going to talk to HR about some early insight programs as I'm about to become a sophomore. Based upon this when should I send a follow up thanking him for taking the time to speak with me. I want to be as appropriate and polite as possible. This was my first legit coffee chat over the phone too.