Writing an email to someone who didn't respond to your last...

Hi all,

Basically, I had written an email to a superior in a group, to try to get into his group. He responded with, how long can you be committed to a specific project, and that if I am devoted etc he will try to help and also to please let him know if I can meet him next week in his office...

I responded that evening which was Tuesday (it's not Friday), about coming in next week, and would love to meet him etc etc...

I have yet to hear anything from him...How long do I have to wait until I can send another email? Do I actually write "Unsure if you saw my last email..."?

Thanks.