What does "by Tuesday" mean?

Last week (Friday), I submitted my resume/portfolio to a company I really want to do an internship for this Summer. The same day, the guy I sent my materials to emailed me a few hours later and told me that if I hadn’t heard anything “by Tuesday”, to please let him know. It’s now Tuesday, and I haven’t heard anything… so do I email him now, or am I supposed to wait through today as well, and if I don’t hear anything, contact him tomorrow?
Thanks!