How long should I wait?

I'm not trying to get weirdly obsessive because I know people have more important things than emailing random people they just met.

But I asked a cute guy at a convenience store for his email address. Well I had someone else ask for me but whatever.. He gave it (keitai address) and I emailed him a day later and within an hr he responded, now he hasn't replied back and I think I might've said something stupid and he no longer wants to talk (or he may be very busy)

I'm not sure if he is a university student and may be busy with his studies (in addition to working), but that's the question I asked in the email.
I know there isn't a set time, I'm just curious how long do you guys think it would take to hear back from him if he was interested in becoming friends?

That's a good question!
How long do you wait for an answer now, a day?
I'm in a similar situation, I too emailed a guy after he told me that he'll visit my country and hopes to meet me here (we've met before in his country). Up to now I didn't got an answer too maybe I have too high expectations..
What I wanted to tell you with that is that it is not an individual case but I think after one week you will not hear anything more from that guy.

Thank you for the reply kizuna.
He replied to me today (2 days later) explaining that he had long hrs at work as he is not a uni student.

Hopefully you will get a response from the guy soon. Good luck :)