Haven't gotten a response to an email?

I write stuff for the school website, so I needed to interview the president of a certain school club. I wrote to him yesterday, and I was pleased when he responded almost instantly saying that he would be glad to be interviewed. I emailed back saying that we could meet sometime between 3:30 and 7 on Thursday at a specific place.

I expected him to get back to me quickly again, but nothing happened. I am on the club email list, and he sent out the weekly club email, so he has clearly been online today. From his previous actions, I expected him to at least respond within the day. Maybe he just missed my email somehow? Or maybe I should take his silence to mean that we're meeting at 3:30? I feel like I should email him again, but I don't know what I should say. Help me, Internet!